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 $33.33   8.549%   $36.1794   $36.18   $36.20   $36.20  
  Purchase #2 $211.96   7.857%   $228.6137   $228.61   $228.60   $228.60  
  Purchase #3 $52.78   3.687%   $54.726   $54.73   $54.75   $54.70  
  Purchase #4 $238.67   9.380%   $261.0572   $261.06   $261.05   $261.10  
  Purchase #5 $226.93   8.578%   $246.3961   $246.40   $246.40   $246.40  
  Purchase #6 $177.55   3.859%   $184.4017   $184.40   $184.40   $184.40  
  Purchase #7 $203.63   5.220%   $214.2595   $214.26   $214.25   $214.30  
  7 purchase totals = $1,144.85       $1,225.6336   $1,225.64   $1,225.65   $1,225.70