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 $218.92   6.779%   $233.7606   $233.76   $233.75   $233.80  
  Purchase #2 $84.47   8.493%   $91.644   $91.64   $91.65   $91.60  
  Purchase #3 $74.33   3.226%   $76.7279   $76.73   $76.75   $76.70  
  Purchase #4 $45.90   9.128%   $50.0898   $50.09   $50.10   $50.10  
  Purchase #5 $138.85   5.281%   $146.1827   $146.18   $146.20   $146.20  
  Purchase #6 $69.75   9.362%   $76.28   $76.28   $76.30   $76.30  
  Purchase #7 $224.92   12.491%   $253.0148   $253.01   $253.00   $253.00  
  7 purchase totals = $857.14       $927.6998   $927.69   $927.75   $927.70