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 $110.68   13.579%   $125.7092   $125.71   $125.70   $125.70  
  Purchase #2 $10.58   3.126%   $10.9107   $10.91   $10.90   $10.90  
  Purchase #3 $200.36   10.601%   $221.6002   $221.60   $221.60   $221.60  
  Purchase #4 $162.70   12.281%   $182.6812   $182.68   $182.70   $182.70  
  Purchase #5 $235.72   11.321%   $262.4059   $262.41   $262.40   $262.40  
  Purchase #6 $98.62   10.795%   $109.266   $109.27   $109.25   $109.30  
  Purchase #7 $165.97   13.419%   $188.2415   $188.24   $188.25   $188.20  
  7 purchase totals = $984.63       $1,100.8147   $1,100.82   $1,100.80   $1,100.80