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 $239.84   12.226%   $269.1628   $269.16   $269.15   $269.20  
  Purchase #2 $104.66   7.344%   $112.3462   $112.35   $112.35   $112.30  
  Purchase #3 $177.55   11.787%   $198.4778   $198.48   $198.50   $198.50  
  Purchase #4 $211.94   6.459%   $225.6292   $225.63   $225.65   $225.60  
  Purchase #5 $22.28   9.833%   $24.4708   $24.47   $24.45   $24.50  
  Purchase #6 $185.90   10.331%   $205.1053   $205.11   $205.10   $205.10  
  Purchase #7 $219.85   6.120%   $233.3048   $233.30   $233.30   $233.30  
  7 purchase totals = $1,162.02       $1,268.4969   $1,268.50   $1,268.50   $1,268.50