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 $205.63   10.168%   $226.5385   $226.54   $226.55   $226.50  
  Purchase #2 $222.61   8.657%   $241.8813   $241.88   $241.90   $241.90  
  Purchase #3 $42.67   12.612%   $48.0515   $48.05   $48.05   $48.10  
  Purchase #4 $243.42   10.810%   $269.7337   $269.73   $269.75   $269.70  
  Purchase #5 $113.55   4.679%   $118.863   $118.86   $118.85   $118.90  
  Purchase #6 $233.89   10.758%   $259.0519   $259.05   $259.05   $259.10  
  Purchase #7 $249.39   9.352%   $272.713   $272.71   $272.70   $272.70  
  7 purchase totals = $1,311.16       $1,436.8329   $1,436.82   $1,436.85   $1,436.90