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 $208.92   12.830%   $235.7244   $235.72   $235.70   $235.70  
  Purchase #2 $126.97   4.155%   $132.2456   $132.25   $132.25   $132.20  
  Purchase #3 $161.36   11.192%   $179.4194   $179.42   $179.40   $179.40  
  Purchase #4 $43.73   10.352%   $48.2569   $48.26   $48.25   $48.30  
  Purchase #5 $91.58   7.256%   $98.225   $98.23   $98.25   $98.20  
  Purchase #6 $62.47   13.243%   $70.7429   $70.74   $70.75   $70.70  
  Purchase #7 $238.64   7.750%   $257.1346   $257.13   $257.15   $257.10  
  7 purchase totals = $933.67       $1,021.7488   $1,021.75   $1,021.75   $1,021.60