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 $245.70   6.638%   $262.0096   $262.01   $262.00   $262.00  
  Purchase #2 $212.63   5.639%   $224.6202   $224.62   $224.60   $224.60  
  Purchase #3 $113.39   6.178%   $120.3952   $120.40   $120.40   $120.40  
  Purchase #4 $116.36   7.123%   $124.6483   $124.65   $124.65   $124.60  
  Purchase #5 $51.67   9.864%   $56.7667   $56.77   $56.75   $56.80  
  Purchase #6 $114.46   5.453%   $120.7015   $120.70   $120.70   $120.70  
  Purchase #7 $23.60   3.819%   $24.5013   $24.50   $24.50   $24.50  
  7 purchase totals = $877.81       $933.6428   $933.65   $933.60   $933.60