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 $224.69   12.669%   $253.156   $253.16   $253.15   $253.20  
  Purchase #2 $84.87   8.674%   $92.2316   $92.23   $92.25   $92.20  
  Purchase #3 $125.37   8.766%   $136.3599   $136.36   $136.35   $136.40  
  Purchase #4 $250.64   7.207%   $268.7036   $268.70   $268.70   $268.70  
  Purchase #5 $57.71   12.842%   $65.1211   $65.12   $65.10   $65.10  
  Purchase #6 $95.78   11.600%   $106.8905   $106.89   $106.90   $106.90  
  Purchase #7 $93.69   6.279%   $99.5728   $99.57   $99.55   $99.60  
  7 purchase totals = $932.75       $1,022.0355   $1,022.03   $1,022.00   $1,022.10