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 $110.67   12.209%   $124.1817   $124.18   $124.20   $124.20  
  Purchase #2 $90.93   6.203%   $96.5704   $96.57   $96.55   $96.60  
  Purchase #3 $96.27   4.631%   $100.7283   $100.73   $100.75   $100.70  
  Purchase #4 $188.86   4.856%   $198.031   $198.03   $198.05   $198.00  
  Purchase #5 $178.99   4.811%   $187.6012   $187.60   $187.60   $187.60  
  Purchase #6 $190.45   8.833%   $207.2724   $207.27   $207.25   $207.30  
  Purchase #7 $230.72   6.463%   $245.6314   $245.63   $245.65   $245.60  
  7 purchase totals = $1,086.89       $1,160.0164   $1,160.01   $1,160.05   $1,160.00