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 $58.89   6.340%   $62.6236   $62.62   $62.60   $62.60  
  Purchase #2 $89.77   12.327%   $100.8359   $100.84   $100.85   $100.80  
  Purchase #3 $203.62   10.461%   $224.9207   $224.92   $224.90   $224.90  
  Purchase #4 $126.91   8.537%   $137.7443   $137.74   $137.75   $137.70  
  Purchase #5 $130.83   5.131%   $137.5429   $137.54   $137.55   $137.50  
  Purchase #6 $250.26   5.871%   $264.9528   $264.95   $264.95   $265.00  
  Purchase #7 $98.53   12.329%   $110.6778   $110.68   $110.70   $110.70  
  7 purchase totals = $958.81       $1,039.2980   $1,039.29   $1,039.30   $1,039.20