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 $201.32   6.558%   $214.5226   $214.52   $214.50   $214.50  
  Purchase #2 $216.81   3.653%   $224.7301   $224.73   $224.75   $224.70  
  Purchase #3 $18.68   11.829%   $20.8897   $20.89   $20.90   $20.90  
  Purchase #4 $19.69   4.260%   $20.5288   $20.53   $20.55   $20.50  
  Purchase #5 $142.80   3.775%   $148.1907   $148.19   $148.20   $148.20  
  Purchase #6 $59.54   4.183%   $62.0306   $62.03   $62.05   $62.00  
  Purchase #7 $120.86   10.288%   $133.2941   $133.29   $133.30   $133.30  
  7 purchase totals = $779.70       $824.1866   $824.18   $824.25   $824.10