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	$155.83	6.453%	$165.8857	$165.89	$165.90	$165.90
Purchase #2	$149.42	3.187%	$154.182	$154.18	$154.20	$154.20
Purchase #3	$234.56	6.376%	$249.5155	$249.52	$249.50	$249.50
Purchase #4	$68.25	4.214%	$71.1261	$71.13	$71.15	$71.10
Purchase #5	$38.98	3.688%	$40.4176	$40.42	$40.40	$40.40
Purchase #6	$73.98	9.179%	$80.7706	$80.77	$80.75	$80.80
Purchase #7	$26.44	7.724%	$28.4822	$28.48	$28.50	$28.50
7 purchase totals =	$747.46		$790.3797	$790.39	$790.40	$790.40