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 $105.93   9.255%   $115.7338   $115.73   $115.75   $115.70  
  Purchase #2 $213.41   12.818%   $240.7649   $240.76   $240.75   $240.80  
  Purchase #3 $92.28   8.289%   $99.9291   $99.93   $99.95   $99.90  
  Purchase #4 $203.44   4.726%   $213.0546   $213.05   $213.05   $213.10  
  Purchase #5 $203.59   11.366%   $226.73   $226.73   $226.75   $226.70  
  Purchase #6 $95.25   11.458%   $106.1637   $106.16   $106.15   $106.20  
  Purchase #7 $157.83   10.687%   $174.6973   $174.70   $174.70   $174.70  
  7 purchase totals = $1,071.73       $1,177.0734   $1,177.06   $1,177.10   $1,177.10