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 $58.53   10.747%   $64.8202   $64.82   $64.80   $64.80  
  Purchase #2 $183.51   7.639%   $197.5283   $197.53   $197.55   $197.50  
  Purchase #3 $36.57   12.658%   $41.199   $41.20   $41.20   $41.20  
  Purchase #4 $111.60   9.282%   $121.9587   $121.96   $121.95   $122.00  
  Purchase #5 $224.87   13.501%   $255.2297   $255.23   $255.25   $255.20  
  Purchase #6 $26.59   3.443%   $27.5055   $27.51   $27.50   $27.50  
  Purchase #7 $70.79   3.162%   $73.0284   $73.03   $73.05   $73.00  
  7 purchase totals = $712.46       $781.2698   $781.28   $781.30   $781.20