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 $199.75   12.819%   $225.356   $225.36   $225.35   $225.40  
  Purchase #2 $47.70   7.850%   $51.4445   $51.44   $51.45   $51.40  
  Purchase #3 $138.30   3.187%   $142.7076   $142.71   $142.70   $142.70  
  Purchase #4 $18.41   5.196%   $19.3666   $19.37   $19.35   $19.40  
  Purchase #5 $17.94   13.242%   $20.3156   $20.32   $20.30   $20.30  
  Purchase #6 $207.27   4.404%   $216.3982   $216.40   $216.40   $216.40  
  Purchase #7 $96.38   11.744%   $107.6989   $107.70   $107.70   $107.70  
  7 purchase totals = $725.75       $783.2874   $783.30   $783.25   $783.30