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 $59.34   11.726%   $66.2982   $66.30   $66.30   $66.30  
  Purchase #2 $33.56   7.572%   $36.1012   $36.10   $36.10   $36.10  
  Purchase #3 $22.75   4.171%   $23.6989   $23.70   $23.70   $23.70  
  Purchase #4 $196.75   10.541%   $217.4894   $217.49   $217.50   $217.50  
  Purchase #5 $42.86   7.233%   $45.9601   $45.96   $45.95   $46.00  
  Purchase #6 $82.39   13.370%   $93.4055   $93.41   $93.40   $93.40  
  Purchase #7 $241.64   6.795%   $258.0594   $258.06   $258.05   $258.10  
  7 purchase totals = $679.29       $741.0127   $741.02   $741.00   $741.10