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	$231.95	13.466%	$263.1844	$263.18	$263.20	$263.20
Purchase #2	$152.96	7.618%	$164.6125	$164.61	$164.60	$164.60
Purchase #3	$145.97	12.858%	$164.7388	$164.74	$164.75	$164.70
Purchase #4	$240.41	12.539%	$270.555	$270.56	$270.55	$270.60
Purchase #5	$47.67	11.778%	$53.2846	$53.28	$53.30	$53.30
Purchase #6	$83.61	7.707%	$90.0538	$90.05	$90.05	$90.10
Purchase #7	$69.65	8.491%	$75.564	$75.56	$75.55	$75.60
7 purchase totals =	$972.22		$1,081.9931	$1,081.98	$1,082.00	$1,082.10