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 $219.52   11.209%   $244.126   $244.13   $244.15   $244.10  
  Purchase #2 $59.45   4.563%   $62.1627   $62.16   $62.15   $62.20  
  Purchase #3 $189.60   3.116%   $195.5079   $195.51   $195.50   $195.50  
  Purchase #4 $114.90   10.872%   $127.3919   $127.39   $127.40   $127.40  
  Purchase #5 $9.27   5.804%   $9.808   $9.81   $9.80   $9.80  
  Purchase #6 $106.59   6.160%   $113.1559   $113.16   $113.15   $113.20  
  Purchase #7 $66.80   9.453%   $73.1146   $73.11   $73.10   $73.10  
  7 purchase totals = $766.13       $825.2670   $825.27   $825.25   $825.30