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 $241.85   7.761%   $260.62   $260.62   $260.60   $260.60  
  Purchase #2 $129.63   8.386%   $140.5008   $140.50   $140.50   $140.50  
  Purchase #3 $186.53   5.838%   $197.4196   $197.42   $197.40   $197.40  
  Purchase #4 $215.66   12.621%   $242.8784   $242.88   $242.90   $242.90  
  Purchase #5 $45.81   8.865%   $49.8711   $49.87   $49.85   $49.90  
  Purchase #6 $246.84   11.642%   $275.5771   $275.58   $275.60   $275.60  
  Purchase #7 $150.27   11.179%   $167.0687   $167.07   $167.05   $167.10  
  7 purchase totals = $1,216.59       $1,333.9357   $1,333.94   $1,333.90   $1,334.00