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 $96.44   8.788%   $104.9151   $104.92   $104.90   $104.90  
  Purchase #2 $14.98   6.342%   $15.93   $15.93   $15.95   $15.90  
  Purchase #3 $33.42   13.587%   $37.9608   $37.96   $37.95   $38.00  
  Purchase #4 $207.76   6.273%   $220.7928   $220.79   $220.80   $220.80  
  Purchase #5 $60.34   4.710%   $63.182   $63.18   $63.20   $63.20  
  Purchase #6 $97.35   10.507%   $107.5786   $107.58   $107.60   $107.60  
  Purchase #7 $168.38   5.720%   $178.0113   $178.01   $178.00   $178.00  
  7 purchase totals = $678.67       $728.3706   $728.37   $728.40   $728.40