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	$151.44	9.592%	$165.9661	$165.97	$165.95	$166.00
Purchase #2	$134.87	9.578%	$147.7878	$147.79	$147.80	$147.80
Purchase #3	$151.99	10.212%	$167.5112	$167.51	$167.50	$167.50
Purchase #4	$246.59	4.820%	$258.4756	$258.48	$258.50	$258.50
Purchase #5	$50.76	11.839%	$56.7695	$56.77	$56.75	$56.80
Purchase #6	$168.51	6.294%	$179.116	$179.12	$179.10	$179.10
Purchase #7	$58.87	10.121%	$64.8282	$64.83	$64.85	$64.80
7 purchase totals =	$963.03		$1,040.4544	$1,040.47	$1,040.45	$1,040.50