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 $58.91   11.605%   $65.7465   $65.75   $65.75   $65.70  
  Purchase #2 $139.51   3.348%   $144.1808   $144.18   $144.20   $144.20  
  Purchase #3 $67.92   4.350%   $70.8745   $70.87   $70.85   $70.90  
  Purchase #4 $164.92   11.799%   $184.3789   $184.38   $184.40   $184.40  
  Purchase #5 $142.68   6.571%   $152.0555   $152.06   $152.05   $152.10  
  Purchase #6 $182.99   5.327%   $192.7379   $192.74   $192.75   $192.70  
  Purchase #7 $189.30   8.488%   $205.3678   $205.37   $205.35   $205.40  
  7 purchase totals = $946.23       $1,015.3419   $1,015.35   $1,015.35   $1,015.40