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 $113.77   3.755%   $118.0421   $118.04   $118.05   $118.00  
  Purchase #2 $218.91   12.552%   $246.3876   $246.39   $246.40   $246.40  
  Purchase #3 $112.60   6.750%   $120.2005   $120.20   $120.20   $120.20  
  Purchase #4 $30.69   7.530%   $33.001   $33.00   $33.00   $33.00  
  Purchase #5 $31.53   13.559%   $35.8052   $35.81   $35.80   $35.80  
  Purchase #6 $20.87   10.122%   $22.9825   $22.98   $23.00   $23.00  
  Purchase #7 $123.79   13.409%   $140.389   $140.39   $140.40   $140.40  
  7 purchase totals = $652.16       $716.8079   $716.81   $716.85   $716.80