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	$93.74	9.854%	$102.9771	$102.98	$103.00	$103.00
Purchase #2	$227.73	10.353%	$251.3069	$251.31	$251.30	$251.30
Purchase #3	$83.66	7.455%	$89.8969	$89.90	$89.90	$89.90
Purchase #4	$123.96	11.132%	$137.7592	$137.76	$137.75	$137.80
Purchase #5	$158.64	8.869%	$172.7098	$172.71	$172.70	$172.70
Purchase #6	$124.61	10.275%	$137.4137	$137.41	$137.40	$137.40
Purchase #7	$230.92	5.794%	$244.2995	$244.30	$244.30	$244.30
7 purchase totals =	$1,043.26		$1,136.3631	$1,136.37	$1,136.35	$1,136.40