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 $60.46   10.786%   $66.9812   $66.98   $67.00   $67.00  
  Purchase #2 $49.36   7.650%   $53.136   $53.14   $53.15   $53.10  
  Purchase #3 $159.43   11.260%   $177.3818   $177.38   $177.40   $177.40  
  Purchase #4 $237.82   9.288%   $259.9087   $259.91   $259.90   $259.90  
  Purchase #5 $225.34   10.843%   $249.7736   $249.77   $249.75   $249.80  
  Purchase #6 $168.63   9.667%   $184.9315   $184.93   $184.95   $184.90  
  Purchase #7 $138.45   5.547%   $146.1298   $146.13   $146.15   $146.10  
  7 purchase totals = $1,039.49       $1,138.2426   $1,138.24   $1,138.30   $1,138.20