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	$66.28	7.190%	$71.0455	$71.05	$71.05	$71.00
Purchase #2	$83.61	13.433%	$94.8413	$94.84	$94.85	$94.80
Purchase #3	$93.98	11.584%	$104.8666	$104.87	$104.85	$104.90
Purchase #4	$71.99	9.521%	$78.8442	$78.84	$78.85	$78.80
Purchase #5	$143.76	10.464%	$158.803	$158.80	$158.80	$158.80
Purchase #6	$38.25	10.516%	$42.2724	$42.27	$42.25	$42.30
Purchase #7	$89.69	6.745%	$95.7396	$95.74	$95.75	$95.70
7 purchase totals =	$587.56		$646.4126	$646.41	$646.40	$646.30