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 $249.55   7.142%   $267.3729   $267.37   $267.35   $267.40  
  Purchase #2 $233.99   11.138%   $260.0518   $260.05   $260.05   $260.10  
  Purchase #3 $119.96   10.403%   $132.4394   $132.44   $132.45   $132.40  
  Purchase #4 $159.54   13.833%   $181.6092   $181.61   $181.60   $181.60  
  Purchase #5 $65.92   11.662%   $73.6076   $73.61   $73.60   $73.60  
  Purchase #6 $70.92   7.851%   $76.4879   $76.49   $76.50   $76.50  
  Purchase #7 $198.89   13.123%   $224.9903   $224.99   $225.00   $225.00  
  7 purchase totals = $1,098.77       $1,216.5591   $1,216.56   $1,216.55   $1,216.60