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 $82.47   12.829%   $93.0501   $93.05   $93.05   $93.10  
  Purchase #2 $53.91   6.453%   $57.3888   $57.39   $57.40   $57.40  
  Purchase #3 $207.94   11.723%   $232.3168   $232.32   $232.30   $232.30  
  Purchase #4 $245.84   6.288%   $261.2984   $261.30   $261.30   $261.30  
  Purchase #5 $204.25   5.696%   $215.8841   $215.88   $215.90   $215.90  
  Purchase #6 $222.51   12.581%   $250.504   $250.50   $250.50   $250.50  
  Purchase #7 $200.96   5.848%   $212.7121   $212.71   $212.70   $212.70  
  7 purchase totals = $1,217.88       $1,323.1543   $1,323.15   $1,323.15   $1,323.20