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 $235.29   13.583%   $267.2494   $267.25   $267.25   $267.20  
  Purchase #2 $144.93   8.464%   $157.1969   $157.20   $157.20   $157.20  
  Purchase #3 $59.77   11.159%   $66.4397   $66.44   $66.45   $66.40  
  Purchase #4 $148.44   7.447%   $159.4943   $159.49   $159.50   $159.50  
  Purchase #5 $246.56   10.233%   $271.7905   $271.79   $271.80   $271.80  
  Purchase #6 $207.94   4.624%   $217.5551   $217.56   $217.55   $217.60  
  Purchase #7 $221.52   13.422%   $251.2524   $251.25   $251.25   $251.30  
  7 purchase totals = $1,264.45       $1,390.9783   $1,390.98   $1,391.00   $1,391.00