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 $141.43   12.521%   $159.1385   $159.14   $159.15   $159.10  
  Purchase #2 $246.89   8.806%   $268.6311   $268.63   $268.65   $268.60  
  Purchase #3 $50.42   11.439%   $56.1875   $56.19   $56.20   $56.20  
  Purchase #4 $151.29   5.459%   $159.5489   $159.55   $159.55   $159.50  
  Purchase #5 $211.47   10.477%   $233.6257   $233.63   $233.65   $233.60  
  Purchase #6 $190.80   9.693%   $209.2942   $209.29   $209.30   $209.30  
  Purchase #7 $118.35   8.269%   $128.1364   $128.14   $128.15   $128.10  
  7 purchase totals = $1,110.65       $1,214.5623   $1,214.57   $1,214.65   $1,214.40