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 $95.75   12.122%   $107.3568   $107.36   $107.35   $107.40  
  Purchase #2 $227.80   5.192%   $239.6274   $239.63   $239.65   $239.60  
  Purchase #3 $44.25   4.397%   $46.1957   $46.20   $46.20   $46.20  
  Purchase #4 $222.96   10.562%   $246.509   $246.51   $246.50   $246.50  
  Purchase #5 $245.37   6.343%   $260.9338   $260.93   $260.95   $260.90  
  Purchase #6 $143.89   3.250%   $148.5664   $148.57   $148.55   $148.60  
  Purchase #7 $186.69   5.496%   $196.9505   $196.95   $196.95   $197.00  
  7 purchase totals = $1,166.71       $1,246.1396   $1,246.15   $1,246.15   $1,246.20