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 $41.80   3.546%   $43.2822   $43.28   $43.30   $43.30  
  Purchase #2 $91.88   4.526%   $96.0385   $96.04   $96.05   $96.00  
  Purchase #3 $103.78   11.547%   $115.7635   $115.76   $115.75   $115.80  
  Purchase #4 $194.96   8.239%   $211.0228   $211.02   $211.00   $211.00  
  Purchase #5 $156.55   13.735%   $178.0521   $178.05   $178.05   $178.10  
  Purchase #6 $74.87   7.705%   $80.6387   $80.64   $80.65   $80.60  
  Purchase #7 $26.63   13.416%   $30.2027   $30.20   $30.20   $30.20  
  7 purchase totals = $690.47       $755.0005   $754.99   $755.00   $755.00