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 $240.57   13.273%   $272.5009   $272.50   $272.50   $272.50  
  Purchase #2 $44.86   4.174%   $46.7325   $46.73   $46.75   $46.70  
  Purchase #3 $96.89   4.779%   $101.5204   $101.52   $101.50   $101.50  
  Purchase #4 $82.54   9.580%   $90.4473   $90.45   $90.45   $90.40  
  Purchase #5 $8.83   10.457%   $9.7534   $9.75   $9.75   $9.80  
  Purchase #6 $41.46   12.487%   $46.6371   $46.64   $46.65   $46.60  
  Purchase #7 $178.98   12.723%   $201.7516   $201.75   $201.75   $201.80  
  7 purchase totals = $694.13       $769.3432   $769.34   $769.35   $769.30