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 $54.62   9.796%   $59.9706   $59.97   $59.95   $60.00  
  Purchase #2 $73.42   12.347%   $82.4852   $82.49   $82.50   $82.50  
  Purchase #3 $59.94   13.584%   $68.0822   $68.08   $68.10   $68.10  
  Purchase #4 $221.70   6.239%   $235.5319   $235.53   $235.55   $235.50  
  Purchase #5 $155.92   8.551%   $169.2527   $169.25   $169.25   $169.30  
  Purchase #6 $50.26   9.633%   $55.1015   $55.10   $55.10   $55.10  
  Purchase #7 $94.32   12.341%   $105.96   $105.96   $105.95   $106.00  
  7 purchase totals = $710.18       $776.3841   $776.38   $776.40   $776.50