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 $209.54   6.769%   $223.7238   $223.72   $223.70   $223.70  
  Purchase #2 $64.79   3.310%   $66.9345   $66.93   $66.95   $66.90  
  Purchase #3 $236.76   3.427%   $244.8738   $244.87   $244.85   $244.90  
  Purchase #4 $181.50   9.136%   $198.0818   $198.08   $198.10   $198.10  
  Purchase #5 $250.86   4.244%   $261.5065   $261.51   $261.50   $261.50  
  Purchase #6 $217.84   3.731%   $225.9676   $225.97   $225.95   $226.00  
  Purchase #7 $129.71   12.777%   $146.283   $146.28   $146.30   $146.30  
  7 purchase totals = $1,291.00       $1,367.3710   $1,367.36   $1,367.35   $1,367.40