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 $125.29   12.230%   $140.613   $140.61   $140.60   $140.60  
  Purchase #2 $102.90   6.751%   $109.8468   $109.85   $109.85   $109.80  
  Purchase #3 $104.95   11.614%   $117.1389   $117.14   $117.15   $117.10  
  Purchase #4 $154.39   4.808%   $161.8131   $161.81   $161.80   $161.80  
  Purchase #5 $238.93   5.868%   $252.9504   $252.95   $252.95   $253.00  
  Purchase #6 $165.43   8.204%   $179.0019   $179.00   $179.00   $179.00  
  Purchase #7 $183.59   11.608%   $204.9011   $204.90   $204.90   $204.90  
  7 purchase totals = $1,075.48       $1,166.2652   $1,166.26   $1,166.25   $1,166.20