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 $54.59   10.211%   $60.1642   $60.16   $60.15   $60.20  
  Purchase #2 $72.95   3.224%   $75.3019   $75.30   $75.30   $75.30  
  Purchase #3 $23.92   13.354%   $27.1143   $27.11   $27.10   $27.10  
  Purchase #4 $34.67   5.360%   $36.5283   $36.53   $36.55   $36.50  
  Purchase #5 $175.52   13.462%   $199.1485   $199.15   $199.15   $199.10  
  Purchase #6 $142.45   13.645%   $161.8873   $161.89   $161.90   $161.90  
  Purchase #7 $112.96   5.348%   $119.0011   $119.00   $119.00   $119.00  
  7 purchase totals = $617.06       $679.1456   $679.14   $679.15   $679.10