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	$143.31	6.807%	$153.0651	$153.07	$153.05	$153.10
Purchase #2	$179.54	9.406%	$196.4275	$196.43	$196.45	$196.40
Purchase #3	$28.76	6.239%	$30.5543	$30.55	$30.55	$30.60
Purchase #4	$82.98	8.499%	$90.0325	$90.03	$90.05	$90.00
Purchase #5	$162.62	9.635%	$178.2884	$178.29	$178.30	$178.30
Purchase #6	$93.80	10.823%	$103.952	$103.95	$103.95	$104.00
Purchase #7	$229.56	3.284%	$237.0988	$237.10	$237.10	$237.10
7 purchase totals =	$920.57		$989.4186	$989.42	$989.45	$989.50