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 $155.33   8.292%   $168.21   $168.21   $168.20   $168.20  
  Purchase #2 $74.46   9.244%   $81.3431   $81.34   $81.35   $81.30  
  Purchase #3 $39.75   4.665%   $41.6043   $41.60   $41.60   $41.60  
  Purchase #4 $26.86   8.679%   $29.1912   $29.19   $29.20   $29.20  
  Purchase #5 $62.80   9.240%   $68.6027   $68.60   $68.60   $68.60  
  Purchase #6 $244.49   6.476%   $260.3232   $260.32   $260.30   $260.30  
  Purchase #7 $184.45   7.554%   $198.3834   $198.38   $198.40   $198.40  
  7 purchase totals = $788.14       $847.6579   $847.64   $847.65   $847.60