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 $94.40   13.638%   $107.2743   $107.27   $107.25   $107.30  
  Purchase #2 $203.63   11.657%   $227.3671   $227.37   $227.35   $227.40  
  Purchase #3 $194.53   12.437%   $218.7237   $218.72   $218.70   $218.70  
  Purchase #4 $88.30   5.657%   $93.2951   $93.30   $93.30   $93.30  
  Purchase #5 $81.31   8.435%   $88.1685   $88.17   $88.15   $88.20  
  Purchase #6 $54.61   9.742%   $59.9301   $59.93   $59.95   $59.90  
  Purchase #7 $63.70   12.573%   $71.709   $71.71   $71.70   $71.70  
  7 purchase totals = $780.48       $866.4678   $866.47   $866.40   $866.50