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 $218.28   11.658%   $243.7271   $243.73   $243.75   $243.70  
  Purchase #2 $112.57   6.169%   $119.5144   $119.51   $119.50   $119.50  
  Purchase #3 $72.64   4.547%   $75.9429   $75.94   $75.95   $75.90  
  Purchase #4 $53.38   13.154%   $60.4016   $60.40   $60.40   $60.40  
  Purchase #5 $202.28   3.666%   $209.6956   $209.70   $209.70   $209.70  
  Purchase #6 $92.36   6.362%   $98.2359   $98.24   $98.25   $98.20  
  Purchase #7 $139.64   11.245%   $155.3425   $155.34   $155.35   $155.30  
  7 purchase totals = $891.15       $962.8600   $962.86   $962.90   $962.70