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 $62.51   4.417%   $65.2711   $65.27   $65.25   $65.30  
  Purchase #2 $119.63   5.317%   $125.9907   $125.99   $126.00   $126.00  
  Purchase #3 $206.41   13.673%   $234.6324   $234.63   $234.65   $234.60  
  Purchase #4 $245.65   12.470%   $276.2826   $276.28   $276.30   $276.30  
  Purchase #5 $33.99   10.566%   $37.5814   $37.58   $37.60   $37.60  
  Purchase #6 $242.65   12.438%   $272.8308   $272.83   $272.85   $272.80  
  Purchase #7 $214.59   5.490%   $226.371   $226.37   $226.35   $226.40  
  7 purchase totals = $1,125.43       $1,238.9600   $1,238.95   $1,239.00   $1,239.00