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 $76.47   3.753%   $79.3399   $79.34   $79.35   $79.30  
  Purchase #2 $231.67   12.844%   $261.4257   $261.43   $261.45   $261.40  
  Purchase #3 $119.58   12.300%   $134.2883   $134.29   $134.30   $134.30  
  Purchase #4 $235.81   7.849%   $254.3187   $254.32   $254.30   $254.30  
  Purchase #5 $27.86   9.422%   $30.485   $30.49   $30.50   $30.50  
  Purchase #6 $146.33   4.563%   $153.007   $153.01   $153.00   $153.00  
  Purchase #7 $103.47   6.789%   $110.4946   $110.49   $110.50   $110.50  
  7 purchase totals = $941.19       $1,023.3592   $1,023.37   $1,023.40   $1,023.30