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	$96.89	8.495%	$105.1208	$105.12	$105.10	$105.10
Purchase #2	$221.38	10.170%	$243.8943	$243.89	$243.90	$243.90
Purchase #3	$200.84	5.422%	$211.7295	$211.73	$211.75	$211.70
Purchase #4	$33.26	6.229%	$35.3318	$35.33	$35.35	$35.30
Purchase #5	$103.42	10.172%	$113.9399	$113.94	$113.95	$113.90
Purchase #6	$14.73	10.433%	$16.2668	$16.27	$16.25	$16.30
Purchase #7	$45.76	13.472%	$51.9248	$51.92	$51.90	$51.90
7 purchase totals =	$716.28		$778.2079	$778.20	$778.20	$778.10