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 $52.43   12.272%   $58.8642   $58.86   $58.85   $58.90  
  Purchase #2 $201.37   13.174%   $227.8985   $227.90   $227.90   $227.90  
  Purchase #3 $9.77   5.337%   $10.2914   $10.29   $10.30   $10.30  
  Purchase #4 $70.76   7.129%   $75.8045   $75.80   $75.80   $75.80  
  Purchase #5 $48.78   9.262%   $53.298   $53.30   $53.30   $53.30  
  Purchase #6 $42.59   12.490%   $47.9095   $47.91   $47.90   $47.90  
  Purchase #7 $227.38   3.833%   $236.0955   $236.10   $236.10   $236.10  
  7 purchase totals = $653.08       $710.1616   $710.16   $710.15   $710.20