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 $11.26   3.567%   $11.6616   $11.66   $11.65   $11.70  
  Purchase #2 $244.72   7.279%   $262.5332   $262.53   $262.55   $262.50  
  Purchase #3 $87.29   12.577%   $98.2685   $98.27   $98.25   $98.30  
  Purchase #4 $248.83   6.867%   $265.9172   $265.92   $265.90   $265.90  
  Purchase #5 $150.84   13.330%   $170.947   $170.95   $170.95   $170.90  
  Purchase #6 $24.93   7.523%   $26.8055   $26.81   $26.80   $26.80  
  Purchase #7 $116.41   4.268%   $121.3784   $121.38   $121.40   $121.40  
  7 purchase totals = $884.28       $957.5114   $957.52   $957.50   $957.50