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 $181.26   11.167%   $201.5013   $201.50   $201.50   $201.50  
  Purchase #2 $242.66   13.608%   $275.6812   $275.68   $275.70   $275.70  
  Purchase #3 $231.39   9.667%   $253.7585   $253.76   $253.75   $253.80  
  Purchase #4 $215.41   5.473%   $227.1994   $227.20   $227.20   $227.20  
  Purchase #5 $87.63   13.826%   $99.7457   $99.75   $99.75   $99.70  
  Purchase #6 $72.86   5.699%   $77.0123   $77.01   $77.00   $77.00  
  Purchase #7 $148.75   9.174%   $162.3963   $162.40   $162.40   $162.40  
  7 purchase totals = $1,179.96       $1,297.2947   $1,297.30   $1,297.30   $1,297.30