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 $224.54   13.681%   $255.2593   $255.26   $255.25   $255.30  
  Purchase #2 $118.56   10.258%   $130.7219   $130.72   $130.70   $130.70  
  Purchase #3 $56.78   8.482%   $61.5961   $61.60   $61.60   $61.60  
  Purchase #4 $149.76   8.375%   $162.3024   $162.30   $162.30   $162.30  
  Purchase #5 $125.74   8.236%   $136.0959   $136.10   $136.10   $136.10  
  Purchase #6 $148.27   7.703%   $159.6912   $159.69   $159.70   $159.70  
  Purchase #7 $87.67   7.817%   $94.5232   $94.52   $94.50   $94.50  
  7 purchase totals = $911.32       $1,000.1900   $1,000.19   $1,000.15   $1,000.20