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 $250.66   5.871%   $265.3762   $265.38   $265.40   $265.40  
  Purchase #2 $68.27   3.313%   $70.5318   $70.53   $70.55   $70.50  
  Purchase #3 $63.82   13.286%   $72.2991   $72.30   $72.30   $72.30  
  Purchase #4 $193.34   6.183%   $205.2942   $205.29   $205.30   $205.30  
  Purchase #5 $68.39   6.736%   $72.9968   $73.00   $73.00   $73.00  
  Purchase #6 $19.94   6.726%   $21.2812   $21.28   $21.30   $21.30  
  Purchase #7 $52.31   7.210%   $56.0816   $56.08   $56.10   $56.10  
  7 purchase totals = $716.73       $763.8609   $763.86   $763.95   $763.90