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	$153.39	10.194%	$169.0266	$169.03	$169.05	$169.00
Purchase #2	$31.31	6.559%	$33.3636	$33.36	$33.35	$33.40
Purchase #3	$117.80	3.164%	$121.5272	$121.53	$121.55	$121.50
Purchase #4	$143.64	13.102%	$162.4597	$162.46	$162.45	$162.50
Purchase #5	$46.60	4.313%	$48.6099	$48.61	$48.60	$48.60
Purchase #6	$110.76	13.663%	$125.8931	$125.89	$125.90	$125.90
Purchase #7	$139.48	13.557%	$158.3893	$158.39	$158.40	$158.40
7 purchase totals =	$742.98		$819.2694	$819.27	$819.30	$819.30