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 $222.51   10.579%   $246.0493   $246.05   $246.05   $246.00  
  Purchase #2 $125.53   3.861%   $130.3767   $130.38   $130.40   $130.40  
  Purchase #3 $34.80   9.847%   $38.2268   $38.23   $38.25   $38.20  
  Purchase #4 $95.65   7.774%   $103.0858   $103.09   $103.10   $103.10  
  Purchase #5 $236.69   10.777%   $262.1981   $262.20   $262.20   $262.20  
  Purchase #6 $189.61   12.631%   $213.5596   $213.56   $213.55   $213.60  
  Purchase #7 $216.26   8.784%   $235.2563   $235.26   $235.25   $235.30  
  7 purchase totals = $1,121.05       $1,228.7526   $1,228.77   $1,228.80   $1,228.80