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 $238.44   12.544%   $268.3499   $268.35   $268.35   $268.30  
  Purchase #2 $214.66   8.773%   $233.4921   $233.49   $233.50   $233.50  
  Purchase #3 $41.45   8.177%   $44.8394   $44.84   $44.85   $44.80  
  Purchase #4 $34.48   7.682%   $37.1288   $37.13   $37.15   $37.10  
  Purchase #5 $93.86   13.145%   $106.1979   $106.20   $106.20   $106.20  
  Purchase #6 $15.64   8.344%   $16.945   $16.95   $16.95   $16.90  
  Purchase #7 $248.32   4.869%   $260.4107   $260.41   $260.40   $260.40  
  7 purchase totals = $886.85       $967.3638   $967.37   $967.40   $967.20