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 $226.43   7.742%   $243.9602   $243.96   $243.95   $244.00  
  Purchase #2 $23.32   13.240%   $26.4076   $26.41   $26.40   $26.40  
  Purchase #3 $56.55   4.588%   $59.1445   $59.14   $59.15   $59.10  
  Purchase #4 $68.80   10.356%   $75.9249   $75.92   $75.90   $75.90  
  Purchase #5 $114.46   11.348%   $127.4489   $127.45   $127.45   $127.40  
  Purchase #6 $85.87   12.355%   $96.4792   $96.48   $96.50   $96.50  
  Purchase #7 $108.38   5.300%   $114.1241   $114.12   $114.10   $114.10  
  7 purchase totals = $683.81       $743.4894   $743.48   $743.45   $743.40