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 $47.27   12.872%   $53.3546   $53.35   $53.35   $53.40  
  Purchase #2 $226.76   3.245%   $234.1184   $234.12   $234.10   $234.10  
  Purchase #3 $93.60   5.749%   $98.9811   $98.98   $99.00   $99.00  
  Purchase #4 $179.26   13.479%   $203.4225   $203.42   $203.40   $203.40  
  Purchase #5 $183.66   7.414%   $197.2766   $197.28   $197.30   $197.30  
  Purchase #6 $88.89   12.384%   $99.8981   $99.90   $99.90   $99.90  
  Purchase #7 $7.79   5.692%   $8.2334   $8.23   $8.25   $8.20  
  7 purchase totals = $827.23       $895.2847   $895.28   $895.30   $895.30