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 $246.68   11.545%   $275.1592   $275.16   $275.15   $275.20  
  Purchase #2 $156.64   10.857%   $173.6464   $173.65   $173.65   $173.60  
  Purchase #3 $90.69   8.860%   $98.7251   $98.73   $98.75   $98.70  
  Purchase #4 $219.77   13.701%   $249.8807   $249.88   $249.90   $249.90  
  Purchase #5 $207.34   7.371%   $222.623   $222.62   $222.60   $222.60  
  Purchase #6 $44.54   12.232%   $49.9881   $49.99   $50.00   $50.00  
  Purchase #7 $54.31   12.760%   $61.24   $61.24   $61.25   $61.20  
  7 purchase totals = $1,019.97       $1,131.2625   $1,131.27   $1,131.30   $1,131.20