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 $86.45   8.302%   $93.6271   $93.63   $93.65   $93.60  
  Purchase #2 $38.75   9.755%   $42.5301   $42.53   $42.55   $42.50  
  Purchase #3 $158.97   9.811%   $174.5665   $174.57   $174.55   $174.60  
  Purchase #4 $173.92   5.576%   $183.6178   $183.62   $183.60   $183.60  
  Purchase #5 $66.76   4.417%   $69.7088   $69.71   $69.70   $69.70  
  Purchase #6 $232.72   11.472%   $259.4176   $259.42   $259.40   $259.40  
  Purchase #7 $185.84   3.397%   $192.153   $192.15   $192.15   $192.20  
  7 purchase totals = $943.41       $1,015.6209   $1,015.63   $1,015.60   $1,015.60