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 $114.54   11.874%   $128.1405   $128.14   $128.15   $128.10  
  Purchase #2 $169.97   9.734%   $186.5149   $186.51   $186.50   $186.50  
  Purchase #3 $51.81   3.824%   $53.7912   $53.79   $53.80   $53.80  
  Purchase #4 $181.36   7.191%   $194.4016   $194.40   $194.40   $194.40  
  Purchase #5 $89.25   6.796%   $95.3154   $95.32   $95.30   $95.30  
  Purchase #6 $91.76   10.288%   $101.2003   $101.20   $101.20   $101.20  
  Purchase #7 $7.34   7.193%   $7.868   $7.87   $7.85   $7.90  
  7 purchase totals = $706.03       $767.2319   $767.23   $767.20   $767.20