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 $160.60   3.589%   $166.3639   $166.36   $166.35   $166.40  
  Purchase #2 $68.79   4.456%   $71.8553   $71.86   $71.85   $71.90  
  Purchase #3 $56.83   5.868%   $60.1648   $60.16   $60.15   $60.20  
  Purchase #4 $233.90   4.615%   $244.6945   $244.69   $244.70   $244.70  
  Purchase #5 $65.41   4.856%   $68.5863   $68.59   $68.60   $68.60  
  Purchase #6 $246.54   3.103%   $254.1901   $254.19   $254.20   $254.20  
  Purchase #7 $221.41   8.770%   $240.8277   $240.83   $240.85   $240.80  
  7 purchase totals = $1,053.48       $1,106.6826   $1,106.68   $1,106.70   $1,106.80