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 $193.68   6.791%   $206.8328   $206.83   $206.85   $206.80  
  Purchase #2 $184.86   12.626%   $208.2004   $208.20   $208.20   $208.20  
  Purchase #3 $59.45   12.165%   $66.6821   $66.68   $66.70   $66.70  
  Purchase #4 $60.37   6.288%   $64.1661   $64.17   $64.15   $64.20  
  Purchase #5 $204.77   4.172%   $213.313   $213.31   $213.30   $213.30  
  Purchase #6 $112.94   5.521%   $119.1754   $119.18   $119.20   $119.20  
  Purchase #7 $107.36   7.285%   $115.1812   $115.18   $115.20   $115.20  
  7 purchase totals = $923.43       $993.5510   $993.55   $993.60   $993.60