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 $42.93   8.491%   $46.5752   $46.58   $46.60   $46.60  
  Purchase #2 $69.61   10.770%   $77.107   $77.11   $77.10   $77.10  
  Purchase #3 $48.75   13.445%   $55.3044   $55.30   $55.30   $55.30  
  Purchase #4 $192.46   8.661%   $209.129   $209.13   $209.15   $209.10  
  Purchase #5 $137.49   7.846%   $148.2775   $148.28   $148.30   $148.30  
  Purchase #6 $199.26   10.858%   $220.8957   $220.90   $220.90   $220.90  
  Purchase #7 $19.67   13.500%   $22.3255   $22.33   $22.35   $22.30  
  7 purchase totals = $710.17       $779.6143   $779.63   $779.70   $779.60