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 $38.74   6.227%   $41.1523   $41.15   $41.15   $41.20  
  Purchase #2 $246.39   6.347%   $262.0284   $262.03   $262.05   $262.00  
  Purchase #3 $180.60   12.549%   $203.2635   $203.26   $203.25   $203.30  
  Purchase #4 $32.92   12.245%   $36.9511   $36.95   $36.95   $37.00  
  Purchase #5 $75.75   3.563%   $78.449   $78.45   $78.45   $78.40  
  Purchase #6 $96.68   8.653%   $105.0457   $105.05   $105.05   $105.00  
  Purchase #7 $227.27   5.568%   $239.9244   $239.92   $239.90   $239.90  
  7 purchase totals = $898.35       $966.8144   $966.81   $966.80   $966.80