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 $122.67   3.248%   $126.6543   $126.65   $126.65   $126.70  
  Purchase #2 $53.41   9.604%   $58.5395   $58.54   $58.55   $58.50  
  Purchase #3 $216.61   11.279%   $241.0414   $241.04   $241.05   $241.00  
  Purchase #4 $167.69   4.751%   $175.657   $175.66   $175.65   $175.70  
  Purchase #5 $231.59   13.184%   $262.1228   $262.12   $262.10   $262.10  
  Purchase #6 $81.63   6.536%   $86.9653   $86.97   $86.95   $87.00  
  Purchase #7 $215.63   10.336%   $237.9175   $237.92   $237.90   $237.90  
  7 purchase totals = $1,089.23       $1,188.8978   $1,188.90   $1,188.85   $1,188.90