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 $68.81   13.714%   $78.2466   $78.25   $78.25   $78.20  
  Purchase #2 $157.26   6.739%   $167.8578   $167.86   $167.85   $167.90  
  Purchase #3 $29.56   3.230%   $30.5148   $30.51   $30.50   $30.50  
  Purchase #4 $218.47   6.106%   $231.8098   $231.81   $231.80   $231.80  
  Purchase #5 $76.87   5.373%   $81.0002   $81.00   $81.00   $81.00  
  Purchase #6 $224.33   10.506%   $247.8981   $247.90   $247.90   $247.90  
  Purchase #7 $125.30   10.406%   $138.3387   $138.34   $138.35   $138.30  
  7 purchase totals = $900.60       $975.6660   $975.67   $975.65   $975.60