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	$90.40	10.515%	$99.9056	$99.91	$99.90	$99.90
Purchase #2	$82.71	11.134%	$91.9189	$91.92	$91.90	$91.90
Purchase #3	$124.42	10.142%	$137.0387	$137.04	$137.05	$137.00
Purchase #4	$242.64	8.253%	$262.6651	$262.67	$262.65	$262.70
Purchase #5	$191.37	6.624%	$204.0463	$204.05	$204.05	$204.00
Purchase #6	$227.93	12.144%	$255.6098	$255.61	$255.60	$255.60
Purchase #7	$148.89	3.164%	$153.6009	$153.60	$153.60	$153.60
7 purchase totals =	$1,108.36		$1,204.7853	$1,204.80	$1,204.75	$1,204.70