Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $141.59   10.691%   $156.7274   $156.73   $156.75   $156.70  
  Purchase #2 $143.92   12.332%   $161.6682   $161.67   $161.65   $161.70  
  Purchase #3 $171.73   3.823%   $178.2952   $178.30   $178.30   $178.30  
  Purchase #4 $186.56   5.790%   $197.3618   $197.36   $197.35   $197.40  
  Purchase #5 $235.36   3.703%   $244.0754   $244.08   $244.10   $244.10  
  Purchase #6 $111.32   11.870%   $124.5337   $124.53   $124.55   $124.50  
  Purchase #7 $135.57   6.759%   $144.7332   $144.73   $144.75   $144.70  
  7 purchase totals = $1,126.05       $1,207.3949   $1,207.40   $1,207.45   $1,207.40