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 $60.62   9.463%   $66.3565   $66.36   $66.35   $66.40  
  Purchase #2 $203.31   6.757%   $217.0477   $217.05   $217.05   $217.00  
  Purchase #3 $48.54   10.363%   $53.5702   $53.57   $53.55   $53.60  
  Purchase #4 $171.55   9.253%   $187.4235   $187.42   $187.40   $187.40  
  Purchase #5 $43.28   3.428%   $44.7636   $44.76   $44.75   $44.80  
  Purchase #6 $24.75   7.492%   $26.6043   $26.60   $26.60   $26.60  
  Purchase #7 $124.30   7.723%   $133.8997   $133.90   $133.90   $133.90  
  7 purchase totals = $676.35       $729.6655   $729.66   $729.60   $729.70