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 $71.43   6.656%   $76.1844   $76.18   $76.20   $76.20  
  Purchase #2 $106.66   9.665%   $116.9687   $116.97   $116.95   $117.00  
  Purchase #3 $58.90   11.519%   $65.6847   $65.68   $65.70   $65.70  
  Purchase #4 $51.38   4.461%   $53.6721   $53.67   $53.65   $53.70  
  Purchase #5 $16.49   12.525%   $18.5554   $18.56   $18.55   $18.60  
  Purchase #6 $46.56   9.655%   $51.0554   $51.06   $51.05   $51.10  
  Purchase #7 $203.98   6.302%   $216.8348   $216.83   $216.85   $216.80  
  7 purchase totals = $555.40       $598.9555   $598.95   $598.95   $599.10