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	$153.38	3.275%	$158.4032	$158.40	$158.40	$158.40
Purchase #2	$179.36	9.677%	$196.7167	$196.72	$196.70	$196.70
Purchase #3	$231.85	3.546%	$240.0714	$240.07	$240.05	$240.10
Purchase #4	$226.86	3.398%	$234.5687	$234.57	$234.55	$234.60
Purchase #5	$70.76	5.269%	$74.4883	$74.49	$74.50	$74.50
Purchase #6	$203.55	5.341%	$214.4216	$214.42	$214.40	$214.40
Purchase #7	$66.43	9.234%	$72.5641	$72.56	$72.55	$72.60
7 purchase totals =	$1,132.19		$1,191.2340	$1,191.23	$1,191.15	$1,191.30