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	$79.40	7.672%	$85.4916	$85.49	$85.50	$85.50
Purchase #2	$122.69	5.462%	$129.3913	$129.39	$129.40	$129.40
Purchase #3	$9.40	9.664%	$10.3084	$10.31	$10.30	$10.30
Purchase #4	$224.46	3.322%	$231.9166	$231.92	$231.90	$231.90
Purchase #5	$176.93	11.142%	$196.6435	$196.64	$196.65	$196.60
Purchase #6	$20.85	6.314%	$22.1665	$22.17	$22.15	$22.20
Purchase #7	$154.82	8.776%	$168.407	$168.41	$168.40	$168.40
7 purchase totals =	$788.55		$844.3249	$844.33	$844.30	$844.30