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 $242.78   8.193%   $262.671   $262.67   $262.65   $262.70  
  Purchase #2 $213.62   4.389%   $222.9958   $223.00   $223.00   $223.00  
  Purchase #3 $221.88   13.575%   $252.0002   $252.00   $252.00   $252.00  
  Purchase #4 $217.59   6.131%   $230.9304   $230.93   $230.95   $230.90  
  Purchase #5 $103.61   6.569%   $110.4161   $110.42   $110.40   $110.40  
  Purchase #6 $98.85   8.196%   $106.9517   $106.95   $106.95   $107.00  
  Purchase #7 $106.57   13.242%   $120.682   $120.68   $120.70   $120.70  
  7 purchase totals = $1,204.90       $1,306.6472   $1,306.65   $1,306.65   $1,306.70