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 $57.44   8.185%   $62.1415   $62.14   $62.15   $62.10  
  Purchase #2 $97.97   4.456%   $102.3355   $102.34   $102.35   $102.30  
  Purchase #3 $220.49   5.261%   $232.09   $232.09   $232.10   $232.10  
  Purchase #4 $185.99   7.407%   $199.7663   $199.77   $199.75   $199.80  
  Purchase #5 $104.78   13.598%   $119.028   $119.03   $119.05   $119.00  
  Purchase #6 $28.98   8.218%   $31.3616   $31.36   $31.35   $31.40  
  Purchase #7 $24.71   3.650%   $25.6119   $25.61   $25.60   $25.60  
  7 purchase totals = $720.36       $772.3348   $772.34   $772.35   $772.30