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 $193.92   8.152%   $209.7284   $209.73   $209.75   $209.70  
  Purchase #2 $173.48   13.738%   $197.3127   $197.31   $197.30   $197.30  
  Purchase #3 $125.63   6.140%   $133.3437   $133.34   $133.35   $133.30  
  Purchase #4 $80.87   12.269%   $90.7919   $90.79   $90.80   $90.80  
  Purchase #5 $188.29   11.697%   $210.3143   $210.31   $210.30   $210.30  
  Purchase #6 $43.92   7.301%   $47.1266   $47.13   $47.15   $47.10  
  Purchase #7 $135.75   7.685%   $146.1824   $146.18   $146.20   $146.20  
  7 purchase totals = $941.86       $1,034.8000   $1,034.79   $1,034.85   $1,034.70