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 $217.51   9.589%   $238.367   $238.37   $238.35   $238.40  
  Purchase #2 $65.77   3.854%   $68.3048   $68.30   $68.30   $68.30  
  Purchase #3 $151.39   10.522%   $167.3193   $167.32   $167.30   $167.30  
  Purchase #4 $151.84   13.371%   $172.1425   $172.14   $172.15   $172.10  
  Purchase #5 $203.78   5.383%   $214.7495   $214.75   $214.75   $214.70  
  Purchase #6 $232.45   11.211%   $258.51   $258.51   $258.50   $258.50  
  Purchase #7 $232.36   5.395%   $244.8958   $244.90   $244.90   $244.90  
  7 purchase totals = $1,255.10       $1,364.2889   $1,364.29   $1,364.25   $1,364.20