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 $238.34   8.231%   $257.9578   $257.96   $257.95   $258.00  
  Purchase #2 $66.77   7.866%   $72.0221   $72.02   $72.00   $72.00  
  Purchase #3 $18.85   4.523%   $19.7026   $19.70   $19.70   $19.70  
  Purchase #4 $59.96   8.569%   $65.098   $65.10   $65.10   $65.10  
  Purchase #5 $194.77   3.127%   $200.8605   $200.86   $200.85   $200.90  
  Purchase #6 $175.96   10.420%   $194.295   $194.30   $194.30   $194.30  
  Purchase #7 $60.99   5.761%   $64.5036   $64.50   $64.50   $64.50  
  7 purchase totals = $815.64       $874.4396   $874.44   $874.40   $874.50