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 $116.74   7.387%   $125.3636   $125.36   $125.35   $125.40  
  Purchase #2 $56.63   5.783%   $59.9049   $59.90   $59.90   $59.90  
  Purchase #3 $27.40   3.568%   $28.3776   $28.38   $28.40   $28.40  
  Purchase #4 $166.49   10.639%   $184.2029   $184.20   $184.20   $184.20  
  Purchase #5 $30.64   10.151%   $33.7503   $33.75   $33.75   $33.80  
  Purchase #6 $247.27   6.762%   $263.9904   $263.99   $264.00   $264.00  
  Purchase #7 $164.67   8.154%   $178.0972   $178.10   $178.10   $178.10  
  7 purchase totals = $809.84       $873.6869   $873.68   $873.70   $873.80