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 $216.70   12.266%   $243.2804   $243.28   $243.30   $243.30  
  Purchase #2 $110.36   8.372%   $119.5993   $119.60   $119.60   $119.60  
  Purchase #3 $169.44   3.592%   $175.5263   $175.53   $175.55   $175.50  
  Purchase #4 $161.93   3.278%   $167.2381   $167.24   $167.25   $167.20  
  Purchase #5 $211.41   6.855%   $225.9022   $225.90   $225.90   $225.90  
  Purchase #6 $250.77   3.251%   $258.9225   $258.92   $258.90   $258.90  
  Purchase #7 $92.69   6.135%   $98.3765   $98.38   $98.40   $98.40  
  7 purchase totals = $1,213.30       $1,288.8453   $1,288.85   $1,288.90   $1,288.80