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	$170.31	7.318%	$182.7733	$182.77	$182.75	$182.80
Purchase #2	$32.44	13.707%	$36.8866	$36.89	$36.90	$36.90
Purchase #3	$235.90	9.154%	$257.4943	$257.49	$257.50	$257.50
Purchase #4	$149.95	11.684%	$167.4702	$167.47	$167.45	$167.50
Purchase #5	$40.64	3.644%	$42.1209	$42.12	$42.10	$42.10
Purchase #6	$214.60	8.224%	$232.2487	$232.25	$232.25	$232.20
Purchase #7	$162.43	5.589%	$171.5082	$171.51	$171.50	$171.50
7 purchase totals =	$1,006.27		$1,090.5022	$1,090.50	$1,090.45	$1,090.50