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	$56.34	3.810%	$58.4866	$58.49	$58.50	$58.50
Purchase #2	$91.54	8.570%	$99.385	$99.39	$99.40	$99.40
Purchase #3	$115.84	12.745%	$130.6038	$130.60	$130.60	$130.60
Purchase #4	$162.39	3.724%	$168.4374	$168.44	$168.45	$168.40
Purchase #5	$211.39	9.405%	$231.2712	$231.27	$231.25	$231.30
Purchase #6	$226.42	11.139%	$251.6409	$251.64	$251.65	$251.60
Purchase #7	$143.30	12.573%	$161.3171	$161.32	$161.30	$161.30
7 purchase totals =	$1,007.22		$1,101.1420	$1,101.15	$1,101.15	$1,101.10