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 $83.79   11.576%   $93.4895   $93.49   $93.50   $93.50  
  Purchase #2 $103.76   13.686%   $117.9606   $117.96   $117.95   $118.00  
  Purchase #3 $211.76   10.308%   $233.5882   $233.59   $233.60   $233.60  
  Purchase #4 $112.65   11.454%   $125.5529   $125.55   $125.55   $125.60  
  Purchase #5 $229.39   7.637%   $246.9085   $246.91   $246.90   $246.90  
  Purchase #6 $138.92   9.858%   $152.6147   $152.61   $152.60   $152.60  
  Purchase #7 $182.26   12.198%   $204.4921   $204.49   $204.50   $204.50  
  7 purchase totals = $1,062.53       $1,174.6065   $1,174.60   $1,174.60   $1,174.70