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 $81.62   13.532%   $92.6648   $92.66   $92.65   $92.70  
  Purchase #2 $191.73   9.389%   $209.7315   $209.73   $209.75   $209.70  
  Purchase #3 $113.44   11.126%   $126.0613   $126.06   $126.05   $126.10  
  Purchase #4 $108.59   11.644%   $121.2342   $121.23   $121.25   $121.20  
  Purchase #5 $13.55   6.128%   $14.3803   $14.38   $14.40   $14.40  
  Purchase #6 $194.79   10.669%   $215.5721   $215.57   $215.55   $215.60  
  Purchase #7 $174.89   3.182%   $180.455   $180.46   $180.45   $180.50  
  7 purchase totals = $878.61       $960.0992   $960.09   $960.10   $960.20