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 $97.79   8.425%   $106.0288   $106.03   $106.05   $106.00  
  Purchase #2 $64.43   3.604%   $66.7521   $66.75   $66.75   $66.80  
  Purchase #3 $215.28   6.692%   $229.6865   $229.69   $229.70   $229.70  
  Purchase #4 $196.95   13.625%   $223.7844   $223.78   $223.80   $223.80  
  Purchase #5 $125.53   5.527%   $132.468   $132.47   $132.45   $132.50  
  Purchase #6 $51.56   7.351%   $55.3502   $55.35   $55.35   $55.40  
  Purchase #7 $93.63   4.659%   $97.9922   $97.99   $98.00   $98.00  
  7 purchase totals = $845.17       $912.0622   $912.06   $912.10   $912.20