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 $66.88   8.569%   $72.6109   $72.61   $72.60   $72.60  
  Purchase #2 $196.27   4.828%   $205.7459   $205.75   $205.75   $205.70  
  Purchase #3 $22.87   4.744%   $23.955   $23.96   $23.95   $24.00  
  Purchase #4 $80.46   11.545%   $89.7491   $89.75   $89.75   $89.70  
  Purchase #5 $157.61   3.259%   $162.7465   $162.75   $162.75   $162.70  
  Purchase #6 $52.55   3.334%   $54.302   $54.30   $54.30   $54.30  
  Purchase #7 $241.44   12.292%   $271.1178   $271.12   $271.10   $271.10  
  7 purchase totals = $818.08       $880.2272   $880.24   $880.20   $880.10