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 $38.52   8.855%   $41.9309   $41.93   $41.95   $41.90  
  Purchase #2 $148.97   11.534%   $166.1522   $166.15   $166.15   $166.20  
  Purchase #3 $30.40   12.223%   $34.1158   $34.12   $34.10   $34.10  
  Purchase #4 $82.74   12.241%   $92.8682   $92.87   $92.85   $92.90  
  Purchase #5 $109.43   6.399%   $116.4324   $116.43   $116.45   $116.40  
  Purchase #6 $43.59   3.116%   $44.9483   $44.95   $44.95   $44.90  
  Purchase #7 $204.61   7.773%   $220.5143   $220.51   $220.50   $220.50  
  7 purchase totals = $658.26       $716.9621   $716.96   $716.95   $716.90