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 $114.84   3.249%   $118.5712   $118.57   $118.55   $118.60  
  Purchase #2 $174.96   10.134%   $192.6904   $192.69   $192.70   $192.70  
  Purchase #3 $5.90   8.334%   $6.3917   $6.39   $6.40   $6.40  
  Purchase #4 $20.48   12.723%   $23.0857   $23.09   $23.10   $23.10  
  Purchase #5 $68.32   6.839%   $72.9924   $72.99   $73.00   $73.00  
  Purchase #6 $81.59   11.202%   $90.7297   $90.73   $90.75   $90.70  
  Purchase #7 $238.82   11.730%   $266.8336   $266.83   $266.85   $266.80  
  7 purchase totals = $704.91       $771.2947   $771.29   $771.35   $771.30