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 $67.64   11.631%   $75.5072   $75.51   $75.50   $75.50  
  Purchase #2 $123.76   4.522%   $129.3564   $129.36   $129.35   $129.40  
  Purchase #3 $111.70   6.432%   $118.8845   $118.88   $118.90   $118.90  
  Purchase #4 $68.55   6.151%   $72.7665   $72.77   $72.75   $72.80  
  Purchase #5 $88.37   5.643%   $93.3567   $93.36   $93.35   $93.40  
  Purchase #6 $130.45   10.506%   $144.1551   $144.16   $144.15   $144.20  
  Purchase #7 $132.87   10.805%   $147.2266   $147.23   $147.25   $147.20  
  7 purchase totals = $723.34       $781.2530   $781.27   $781.25   $781.40