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	$48.73	8.868%	$53.0514	$53.05	$53.05	$53.10
Purchase #2	$45.45	6.509%	$48.4083	$48.41	$48.40	$48.40
Purchase #3	$223.27	3.528%	$231.147	$231.15	$231.15	$231.10
Purchase #4	$119.46	3.515%	$123.659	$123.66	$123.65	$123.70
Purchase #5	$151.35	6.130%	$160.6278	$160.63	$160.65	$160.60
Purchase #6	$119.62	9.632%	$131.1418	$131.14	$131.15	$131.10
Purchase #7	$85.72	4.285%	$89.3931	$89.39	$89.40	$89.40
7 purchase totals =	$793.60		$837.4284	$837.43	$837.45	$837.40