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 $83.64   4.578%   $87.469   $87.47   $87.45   $87.50  
  Purchase #2 $149.85   6.742%   $159.9529   $159.95   $159.95   $160.00  
  Purchase #3 $22.77   9.548%   $24.9441   $24.94   $24.95   $24.90  
  Purchase #4 $20.85   12.333%   $23.4214   $23.42   $23.40   $23.40  
  Purchase #5 $124.32   9.291%   $135.8706   $135.87   $135.85   $135.90  
  Purchase #6 $24.55   12.872%   $27.7101   $27.71   $27.70   $27.70  
  Purchase #7 $133.82   13.784%   $152.2657   $152.27   $152.25   $152.30  
  7 purchase totals = $559.80       $611.6338   $611.63   $611.55   $611.70