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 $155.30   9.328%   $169.7864   $169.79   $169.80   $169.80  
  Purchase #2 $194.59   8.377%   $210.8908   $210.89   $210.90   $210.90  
  Purchase #3 $75.26   12.536%   $84.6946   $84.69   $84.70   $84.70  
  Purchase #4 $16.80   13.390%   $19.0495   $19.05   $19.05   $19.00  
  Purchase #5 $194.91   9.534%   $213.4927   $213.49   $213.50   $213.50  
  Purchase #6 $78.33   8.565%   $85.039   $85.04   $85.05   $85.00  
  Purchase #7 $30.39   13.252%   $34.4173   $34.42   $34.40   $34.40  
  7 purchase totals = $745.58       $817.3703   $817.37   $817.40   $817.30