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 $152.91   10.614%   $169.1399   $169.14   $169.15   $169.10  
  Purchase #2 $202.39   11.718%   $226.1061   $226.11   $226.10   $226.10  
  Purchase #3 $100.35   4.519%   $104.8848   $104.88   $104.90   $104.90  
  Purchase #4 $182.83   5.193%   $192.3244   $192.32   $192.30   $192.30  
  Purchase #5 $233.78   3.297%   $241.4877   $241.49   $241.50   $241.50  
  Purchase #6 $207.30   3.661%   $214.8893   $214.89   $214.90   $214.90  
  Purchase #7 $83.70   10.274%   $92.2993   $92.30   $92.30   $92.30  
  7 purchase totals = $1,163.26       $1,241.1315   $1,241.13   $1,241.15   $1,241.10