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	$42.50	6.225%	$45.1456	$45.15	$45.15	$45.10
Purchase #2	$214.93	5.233%	$226.1773	$226.18	$226.20	$226.20
Purchase #3	$154.92	3.657%	$160.5854	$160.59	$160.60	$160.60
Purchase #4	$168.74	3.441%	$174.5463	$174.55	$174.55	$174.50
Purchase #5	$234.27	12.740%	$264.116	$264.12	$264.10	$264.10
Purchase #6	$20.66	4.129%	$21.5131	$21.51	$21.50	$21.50
Purchase #7	$20.76	9.697%	$22.7731	$22.77	$22.75	$22.80
7 purchase totals =	$856.78		$914.8568	$914.87	$914.85	$914.80