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 $245.41   8.135%   $265.3741   $265.37   $265.35   $265.40  
  Purchase #2 $149.35   13.198%   $169.0612   $169.06   $169.05   $169.10  
  Purchase #3 $76.38   8.702%   $83.0266   $83.03   $83.05   $83.00  
  Purchase #4 $8.28   12.785%   $9.3386   $9.34   $9.35   $9.30  
  Purchase #5 $164.34   11.151%   $182.6656   $182.67   $182.65   $182.70  
  Purchase #6 $148.69   7.158%   $159.3332   $159.33   $159.35   $159.30  
  Purchase #7 $78.53   13.167%   $88.87   $88.87   $88.85   $88.90  
  7 purchase totals = $870.98       $957.6693   $957.67   $957.65   $957.70