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 $45.88   5.134%   $48.2355   $48.24   $48.25   $48.20  
  Purchase #2 $94.64   4.172%   $98.5884   $98.59   $98.60   $98.60  
  Purchase #3 $109.59   5.132%   $115.2142   $115.21   $115.20   $115.20  
  Purchase #4 $170.81   9.819%   $187.5818   $187.58   $187.60   $187.60  
  Purchase #5 $33.25   6.567%   $35.4335   $35.43   $35.45   $35.40  
  Purchase #6 $161.92   8.635%   $175.9018   $175.90   $175.90   $175.90  
  Purchase #7 $167.59   7.566%   $180.2699   $180.27   $180.25   $180.30  
  7 purchase totals = $783.68       $841.2251   $841.22   $841.25   $841.20