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 $97.61   9.174%   $106.5647   $106.56   $106.55   $106.60  
  Purchase #2 $227.87   7.681%   $245.3727   $245.37   $245.35   $245.40  
  Purchase #3 $119.74   6.203%   $127.1675   $127.17   $127.15   $127.20  
  Purchase #4 $22.66   8.763%   $24.6457   $24.65   $24.65   $24.60  
  Purchase #5 $162.69   6.254%   $172.8646   $172.86   $172.85   $172.90  
  Purchase #6 $126.45   3.870%   $131.3436   $131.34   $131.35   $131.30  
  Purchase #7 $14.63   6.323%   $15.5551   $15.56   $15.55   $15.60  
  7 purchase totals = $771.65       $823.5139   $823.51   $823.45   $823.60