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	$62.96	6.856%	$67.2765	$67.28	$67.30	$67.30
Purchase #2	$214.76	13.196%	$243.0997	$243.10	$243.10	$243.10
Purchase #3	$19.54	13.804%	$22.2373	$22.24	$22.25	$22.20
Purchase #4	$205.74	11.142%	$228.6636	$228.66	$228.65	$228.70
Purchase #5	$127.37	9.204%	$139.0931	$139.09	$139.10	$139.10
Purchase #6	$151.62	11.427%	$168.9456	$168.95	$168.95	$168.90
Purchase #7	$221.65	4.400%	$231.4026	$231.40	$231.40	$231.40
7 purchase totals =	$1,003.64		$1,100.7184	$1,100.72	$1,100.75	$1,100.70