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 $125.25   6.361%   $133.2172   $133.22   $133.20   $133.20  
  Purchase #2 $162.73   9.777%   $178.6401   $178.64   $178.65   $178.60  
  Purchase #3 $60.93   12.505%   $68.5493   $68.55   $68.55   $68.50  
  Purchase #4 $57.46   6.858%   $61.4006   $61.40   $61.40   $61.40  
  Purchase #5 $200.75   7.631%   $216.0692   $216.07   $216.05   $216.10  
  Purchase #6 $214.76   7.325%   $230.4912   $230.49   $230.50   $230.50  
  Purchase #7 $24.39   7.788%   $26.2895   $26.29   $26.30   $26.30  
  7 purchase totals = $846.27       $914.6571   $914.66   $914.65   $914.60