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	$79.76	12.191%	$89.4835	$89.48	$89.50	$89.50
Purchase #2	$49.68	8.333%	$53.8198	$53.82	$53.80	$53.80
Purchase #3	$181.30	3.784%	$188.1604	$188.16	$188.15	$188.20
Purchase #4	$143.92	4.315%	$150.1301	$150.13	$150.15	$150.10
Purchase #5	$160.65	9.618%	$176.1013	$176.10	$176.10	$176.10
Purchase #6	$205.43	13.590%	$233.3479	$233.35	$233.35	$233.30
Purchase #7	$192.46	5.143%	$202.3582	$202.36	$202.35	$202.40
7 purchase totals =	$1,013.20		$1,093.4012	$1,093.40	$1,093.40	$1,093.40