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 $176.76   11.757%   $197.5417   $197.54   $197.55   $197.50  
  Purchase #2 $79.65   3.194%   $82.194   $82.19   $82.20   $82.20  
  Purchase #3 $166.38   9.802%   $182.6886   $182.69   $182.70   $182.70  
  Purchase #4 $249.94   10.524%   $276.2437   $276.24   $276.25   $276.20  
  Purchase #5 $230.50   12.830%   $260.0732   $260.07   $260.05   $260.10  
  Purchase #6 $139.26   10.676%   $154.1274   $154.13   $154.15   $154.10  
  Purchase #7 $170.85   5.273%   $179.8589   $179.86   $179.85   $179.90  
  7 purchase totals = $1,213.34       $1,332.7275   $1,332.72   $1,332.75   $1,332.70