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 $75.53   11.247%   $84.0249   $84.02   $84.00   $84.00  
  Purchase #2 $209.69   9.352%   $229.3002   $229.30   $229.30   $229.30  
  Purchase #3 $79.85   10.795%   $88.4698   $88.47   $88.45   $88.50  
  Purchase #4 $133.33   13.252%   $150.9989   $151.00   $151.00   $151.00  
  Purchase #5 $86.33   12.366%   $97.0056   $97.01   $97.00   $97.00  
  Purchase #6 $200.53   12.142%   $224.8784   $224.88   $224.90   $224.90  
  Purchase #7 $155.42   11.727%   $173.6461   $173.65   $173.65   $173.60  
  7 purchase totals = $940.68       $1,048.3239   $1,048.33   $1,048.30   $1,048.30