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 $217.53   4.233%   $226.738   $226.74   $226.75   $226.70  
  Purchase #2 $183.73   6.122%   $194.978   $194.98   $195.00   $195.00  
  Purchase #3 $163.45   7.633%   $175.9261   $175.93   $175.95   $175.90  
  Purchase #4 $236.51   6.804%   $252.6021   $252.60   $252.60   $252.60  
  Purchase #5 $8.77   6.362%   $9.3279   $9.33   $9.35   $9.30  
  Purchase #6 $33.99   11.531%   $37.9094   $37.91   $37.90   $37.90  
  Purchase #7 $246.30   8.373%   $266.9227   $266.92   $266.90   $266.90  
  7 purchase totals = $1,090.28       $1,164.4042   $1,164.41   $1,164.45   $1,164.30