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 $234.87   3.726%   $243.6213   $243.62   $243.60   $243.60  
  Purchase #2 $109.57   3.646%   $113.5649   $113.56   $113.55   $113.60  
  Purchase #3 $184.68   8.807%   $200.9448   $200.94   $200.95   $200.90  
  Purchase #4 $221.27   9.176%   $241.5737   $241.57   $241.55   $241.60  
  Purchase #5 $250.87   9.536%   $274.793   $274.79   $274.80   $274.80  
  Purchase #6 $158.78   6.526%   $169.142   $169.14   $169.15   $169.10  
  Purchase #7 $246.78   6.125%   $261.8953   $261.90   $261.90   $261.90  
  7 purchase totals = $1,406.82       $1,505.5350   $1,505.52   $1,505.50   $1,505.50