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	$12.28	8.304%	$13.2997	$13.30	$13.30	$13.30
Purchase #2	$92.81	13.547%	$105.383	$105.38	$105.40	$105.40
Purchase #3	$23.91	4.624%	$25.0156	$25.02	$25.00	$25.00
Purchase #4	$85.63	6.275%	$91.0033	$91.00	$91.00	$91.00
Purchase #5	$98.65	12.873%	$111.3492	$111.35	$111.35	$111.30
Purchase #6	$36.42	13.510%	$41.3403	$41.34	$41.35	$41.30
Purchase #7	$13.30	6.332%	$14.1422	$14.14	$14.15	$14.10
7 purchase totals =	$363.00		$401.5333	$401.53	$401.55	$401.40