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	$174.77	8.322%	$189.3144	$189.31	$189.30	$189.30
Purchase #2	$208.52	11.661%	$232.8355	$232.84	$232.85	$232.80
Purchase #3	$106.54	4.748%	$111.5985	$111.60	$111.60	$111.60
Purchase #4	$79.30	4.694%	$83.0223	$83.02	$83.00	$83.00
Purchase #5	$142.40	13.315%	$161.3606	$161.36	$161.35	$161.40
Purchase #6	$85.53	4.633%	$89.4926	$89.49	$89.50	$89.50
Purchase #7	$105.75	10.206%	$116.5428	$116.54	$116.55	$116.50
7 purchase totals =	$902.81		$984.1667	$984.16	$984.15	$984.10