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 $244.38   9.721%   $268.1362   $268.14   $268.15   $268.10  
  Purchase #2 $62.95   6.335%   $66.9379   $66.94   $66.95   $66.90  
  Purchase #3 $106.92   4.770%   $112.0201   $112.02   $112.00   $112.00  
  Purchase #4 $134.63   10.577%   $148.8698   $148.87   $148.85   $148.90  
  Purchase #5 $133.90   13.178%   $151.5453   $151.55   $151.55   $151.50  
  Purchase #6 $123.47   12.398%   $138.7778   $138.78   $138.80   $138.80  
  Purchase #7 $158.90   4.351%   $165.8137   $165.81   $165.80   $165.80  
  7 purchase totals = $965.15       $1,052.1008   $1,052.11   $1,052.10   $1,052.00