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	$18.33	9.810%	$20.1282	$20.13	$20.15	$20.10
Purchase #2	$223.92	8.538%	$243.0383	$243.04	$243.05	$243.00
Purchase #3	$180.74	9.212%	$197.3898	$197.39	$197.40	$197.40
Purchase #4	$158.37	11.623%	$176.7773	$176.78	$176.80	$176.80
Purchase #5	$127.30	9.464%	$139.3477	$139.35	$139.35	$139.30
Purchase #6	$202.89	13.561%	$230.4039	$230.40	$230.40	$230.40
Purchase #7	$168.40	12.417%	$189.3102	$189.31	$189.30	$189.30
7 purchase totals =	$1,079.95		$1,196.3954	$1,196.40	$1,196.45	$1,196.30