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 $39.37   9.135%   $42.9664   $42.97   $42.95   $43.00  
  Purchase #2 $130.88   4.176%   $136.3455   $136.35   $136.35   $136.30  
  Purchase #3 $71.50   5.583%   $75.4918   $75.49   $75.50   $75.50  
  Purchase #4 $205.79   4.139%   $214.3076   $214.31   $214.30   $214.30  
  Purchase #5 $29.64   9.737%   $32.526   $32.53   $32.55   $32.50  
  Purchase #6 $195.87   8.781%   $213.0693   $213.07   $213.05   $213.10  
  Purchase #7 $68.59   7.289%   $73.5895   $73.59   $73.60   $73.60  
  7 purchase totals = $741.64       $788.2961   $788.31   $788.30   $788.30