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 $34.80   10.787%   $38.5539   $38.55   $38.55   $38.60  
  Purchase #2 $213.77   9.716%   $234.5399   $234.54   $234.55   $234.50  
  Purchase #3 $140.82   7.761%   $151.749   $151.75   $151.75   $151.70  
  Purchase #4 $144.77   11.234%   $161.0335   $161.03   $161.05   $161.00  
  Purchase #5 $48.75   11.138%   $54.1798   $54.18   $54.20   $54.20  
  Purchase #6 $107.27   11.142%   $119.222   $119.22   $119.20   $119.20  
  Purchase #7 $176.26   11.112%   $195.846   $195.85   $195.85   $195.80  
  7 purchase totals = $866.44       $955.1241   $955.12   $955.15   $955.00