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 $208.99   5.629%   $220.754   $220.75   $220.75   $220.80  
  Purchase #2 $15.60   13.378%   $17.687   $17.69   $17.70   $17.70  
  Purchase #3 $91.89   13.551%   $104.342   $104.34   $104.35   $104.30  
  Purchase #4 $211.99   11.637%   $236.6593   $236.66   $236.65   $236.70  
  Purchase #5 $207.60   7.475%   $223.1181   $223.12   $223.10   $223.10  
  Purchase #6 $144.39   12.367%   $162.2467   $162.25   $162.25   $162.20  
  Purchase #7 $61.99   10.343%   $68.4016   $68.40   $68.40   $68.40  
  7 purchase totals = $942.45       $1,033.2087   $1,033.21   $1,033.20   $1,033.20