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 $203.69   10.413%   $224.9002   $224.90   $224.90   $224.90  
  Purchase #2 $52.34   11.187%   $58.1953   $58.20   $58.20   $58.20  
  Purchase #3 $159.73   5.182%   $168.0072   $168.01   $168.00   $168.00  
  Purchase #4 $133.48   3.458%   $138.0957   $138.10   $138.10   $138.10  
  Purchase #5 $66.93   11.696%   $74.7581   $74.76   $74.75   $74.80  
  Purchase #6 $178.61   6.874%   $190.8877   $190.89   $190.90   $190.90  
  Purchase #7 $159.91   7.468%   $171.8521   $171.85   $171.85   $171.90  
  7 purchase totals = $954.69       $1,026.6963   $1,026.71   $1,026.70   $1,026.80