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 $58.42   6.176%   $62.028   $62.03   $62.05   $62.00  
  Purchase #2 $70.78   13.385%   $80.2539   $80.25   $80.25   $80.30  
  Purchase #3 $176.49   10.228%   $194.5414   $194.54   $194.55   $194.50  
  Purchase #4 $180.54   7.634%   $194.3224   $194.32   $194.30   $194.30  
  Purchase #5 $175.27   9.752%   $192.3623   $192.36   $192.35   $192.40  
  Purchase #6 $193.74   11.458%   $215.9387   $215.94   $215.95   $215.90  
  Purchase #7 $127.71   11.352%   $142.2076   $142.21   $142.20   $142.20  
  7 purchase totals = $982.95       $1,081.6543   $1,081.65   $1,081.65   $1,081.60