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 $43.84   10.732%   $48.5449   $48.54   $48.55   $48.50  
  Purchase #2 $110.71   9.539%   $121.2706   $121.27   $121.25   $121.30  
  Purchase #3 $155.68   7.533%   $167.4074   $167.41   $167.40   $167.40  
  Purchase #4 $149.28   3.346%   $154.2749   $154.27   $154.25   $154.30  
  Purchase #5 $153.99   5.247%   $162.0699   $162.07   $162.05   $162.10  
  Purchase #6 $79.85   12.204%   $89.5949   $89.59   $89.60   $89.60  
  Purchase #7 $74.31   7.781%   $80.0921   $80.09   $80.10   $80.10  
  7 purchase totals = $767.66       $823.2547   $823.24   $823.20   $823.30