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	$39.93	12.107%	$44.7643	$44.76	$44.75	$44.80
Purchase #2	$141.34	3.215%	$145.8841	$145.88	$145.90	$145.90
Purchase #3	$37.91	7.278%	$40.6691	$40.67	$40.65	$40.70
Purchase #4	$201.93	3.841%	$209.6861	$209.69	$209.70	$209.70
Purchase #5	$189.49	12.151%	$212.5149	$212.51	$212.50	$212.50
Purchase #6	$173.58	7.426%	$186.4701	$186.47	$186.45	$186.50
Purchase #7	$37.42	13.382%	$42.4275	$42.43	$42.45	$42.40
7 purchase totals =	$821.60		$882.4161	$882.41	$882.40	$882.50