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 $23.48   3.312%   $24.2577   $24.26   $24.25   $24.30  
  Purchase #2 $230.92   4.236%   $240.7018   $240.70   $240.70   $240.70  
  Purchase #3 $243.99   11.236%   $271.4047   $271.40   $271.40   $271.40  
  Purchase #4 $73.26   4.700%   $76.7032   $76.70   $76.70   $76.70  
  Purchase #5 $158.32   8.318%   $171.4891   $171.49   $171.50   $171.50  
  Purchase #6 $9.38   6.836%   $10.0212   $10.02   $10.00   $10.00  
  Purchase #7 $120.40   8.592%   $130.7448   $130.74   $130.75   $130.70  
  7 purchase totals = $859.75       $925.3225   $925.31   $925.30   $925.30