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 $245.71   9.739%   $269.6397   $269.64   $269.65   $269.60  
  Purchase #2 $190.55   10.556%   $210.6645   $210.66   $210.65   $210.70  
  Purchase #3 $190.92   8.569%   $207.2799   $207.28   $207.30   $207.30  
  Purchase #4 $217.82   7.474%   $234.0999   $234.10   $234.10   $234.10  
  Purchase #5 $13.27   6.634%   $14.1503   $14.15   $14.15   $14.20  
  Purchase #6 $204.56   10.528%   $226.0961   $226.10   $226.10   $226.10  
  Purchase #7 $203.74   7.602%   $219.2283   $219.23   $219.25   $219.20  
  7 purchase totals = $1,266.57       $1,381.1587   $1,381.16   $1,381.20   $1,381.20