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 $212.91   6.208%   $226.1275   $226.13   $226.15   $226.10  
  Purchase #2 $248.37   7.865%   $267.9043   $267.90   $267.90   $267.90  
  Purchase #3 $112.46   3.152%   $116.0047   $116.00   $116.00   $116.00  
  Purchase #4 $32.38   4.198%   $33.7393   $33.74   $33.75   $33.70  
  Purchase #5 $68.67   8.519%   $74.52   $74.52   $74.50   $74.50  
  Purchase #6 $188.72   5.815%   $199.6941   $199.69   $199.70   $199.70  
  Purchase #7 $37.40   5.251%   $39.3639   $39.36   $39.35   $39.40  
  7 purchase totals = $900.91       $957.3538   $957.34   $957.35   $957.30