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 $57.43   9.386%   $62.8204   $62.82   $62.80   $62.80  
  Purchase #2 $41.47   13.183%   $46.937   $46.94   $46.95   $46.90  
  Purchase #3 $25.76   4.275%   $26.8612   $26.86   $26.85   $26.90  
  Purchase #4 $117.47   5.540%   $123.9778   $123.98   $124.00   $124.00  
  Purchase #5 $81.58   12.581%   $91.8436   $91.84   $91.85   $91.80  
  Purchase #6 $111.39   6.794%   $118.9578   $118.96   $118.95   $119.00  
  Purchase #7 $110.37   13.532%   $125.3053   $125.31   $125.30   $125.30  
  7 purchase totals = $545.47       $596.7031   $596.71   $596.70   $596.70