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	$37.60	13.590%	$42.7098	$42.71	$42.70	$42.70
Purchase #2	$32.36	8.647%	$35.1582	$35.16	$35.15	$35.20
Purchase #3	$136.88	3.846%	$142.1444	$142.14	$142.15	$142.10
Purchase #4	$69.56	6.164%	$73.8477	$73.85	$73.85	$73.80
Purchase #5	$236.44	7.482%	$254.1304	$254.13	$254.15	$254.10
Purchase #6	$122.71	13.600%	$139.3986	$139.40	$139.40	$139.40
Purchase #7	$164.58	11.695%	$183.8276	$183.83	$183.85	$183.80
7 purchase totals =	$800.13		$871.2167	$871.22	$871.25	$871.10