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	$95.74	9.166%	$104.5155	$104.52	$104.50	$104.50
Purchase #2	$148.31	11.430%	$165.2618	$165.26	$165.25	$165.30
Purchase #3	$180.95	8.664%	$196.6275	$196.63	$196.65	$196.60
Purchase #4	$122.73	3.480%	$127.001	$127.00	$127.00	$127.00
Purchase #5	$166.80	11.480%	$185.9486	$185.95	$185.95	$185.90
Purchase #6	$43.35	6.476%	$46.1573	$46.16	$46.15	$46.20
Purchase #7	$65.66	12.871%	$74.1111	$74.11	$74.10	$74.10
7 purchase totals =	$823.54		$899.6228	$899.63	$899.60	$899.60