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 $183.59   11.159%   $204.0768   $204.08   $204.10   $204.10  
  Purchase #2 $121.80   12.524%   $137.0542   $137.05   $137.05   $137.10  
  Purchase #3 $188.55   3.277%   $194.7288   $194.73   $194.75   $194.70  
  Purchase #4 $247.46   11.349%   $275.5442   $275.54   $275.55   $275.50  
  Purchase #5 $213.35   10.508%   $235.7688   $235.77   $235.75   $235.80  
  Purchase #6 $181.39   3.156%   $187.1147   $187.11   $187.10   $187.10  
  Purchase #7 $128.59   3.809%   $133.488   $133.49   $133.50   $133.50  
  7 purchase totals = $1,264.73       $1,367.7755   $1,367.77   $1,367.80   $1,367.80