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 $242.28   4.708%   $253.6865   $253.69   $253.70   $253.70  
  Purchase #2 $139.41   7.223%   $149.4796   $149.48   $149.50   $149.50  
  Purchase #3 $31.46   11.523%   $35.0851   $35.09   $35.10   $35.10  
  Purchase #4 $207.73   8.607%   $225.6093   $225.61   $225.60   $225.60  
  Purchase #5 $109.96   7.449%   $118.1509   $118.15   $118.15   $118.20  
  Purchase #6 $169.35   4.504%   $176.9775   $176.98   $177.00   $177.00  
  Purchase #7 $5.77   8.136%   $6.2394   $6.24   $6.25   $6.20  
  7 purchase totals = $905.96       $965.2283   $965.24   $965.30   $965.30