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 $65.79   13.271%   $74.521   $74.52   $74.50   $74.50  
  Purchase #2 $62.46   3.631%   $64.7279   $64.73   $64.75   $64.70  
  Purchase #3 $22.75   10.509%   $25.1408   $25.14   $25.15   $25.10  
  Purchase #4 $118.36   6.865%   $126.4854   $126.49   $126.50   $126.50  
  Purchase #5 $45.33   4.421%   $47.334   $47.33   $47.35   $47.30  
  Purchase #6 $184.76   5.422%   $194.7777   $194.78   $194.80   $194.80  
  Purchase #7 $219.85   6.323%   $233.7511   $233.75   $233.75   $233.80  
  7 purchase totals = $719.30       $766.7379   $766.74   $766.80   $766.70