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 $246.51   11.708%   $275.3714   $275.37   $275.35   $275.40  
  Purchase #2 $111.81   12.119%   $125.3603   $125.36   $125.35   $125.40  
  Purchase #3 $174.38   12.303%   $195.834   $195.83   $195.85   $195.80  
  Purchase #4 $91.38   5.682%   $96.5722   $96.57   $96.55   $96.60  
  Purchase #5 $95.35   8.174%   $103.1439   $103.14   $103.15   $103.10  
  Purchase #6 $230.48   10.104%   $253.7677   $253.77   $253.75   $253.80  
  Purchase #7 $185.94   13.492%   $211.027   $211.03   $211.05   $211.00  
  7 purchase totals = $1,135.85       $1,261.0765   $1,261.07   $1,261.05   $1,261.10