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 $214.93   13.211%   $243.3244   $243.32   $243.30   $243.30  
  Purchase #2 $207.95   9.130%   $226.9358   $226.94   $226.95   $226.90  
  Purchase #3 $74.38   9.472%   $81.4253   $81.43   $81.45   $81.40  
  Purchase #4 $13.78   5.349%   $14.5171   $14.52   $14.50   $14.50  
  Purchase #5 $248.48   6.241%   $263.9876   $263.99   $264.00   $264.00  
  Purchase #6 $143.81   10.142%   $158.3952   $158.40   $158.40   $158.40  
  Purchase #7 $165.86   7.732%   $178.6843   $178.68   $178.70   $178.70  
  7 purchase totals = $1,069.19       $1,167.2697   $1,167.28   $1,167.30   $1,167.20