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 $129.82   10.693%   $143.7017   $143.70   $143.70   $143.70  
  Purchase #2 $158.48   13.323%   $179.5943   $179.59   $179.60   $179.60  
  Purchase #3 $185.89   3.806%   $192.965   $192.97   $192.95   $193.00  
  Purchase #4 $66.28   8.350%   $71.8144   $71.81   $71.80   $71.80  
  Purchase #5 $232.71   6.303%   $247.3777   $247.38   $247.40   $247.40  
  Purchase #6 $101.75   10.823%   $112.7624   $112.76   $112.75   $112.80  
  Purchase #7 $206.71   3.127%   $213.1738   $213.17   $213.15   $213.20  
  7 purchase totals = $1,081.64       $1,161.3893   $1,161.38   $1,161.35   $1,161.50