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	$6.79	3.584%	$7.0334	$7.03	$7.05	$7.00
Purchase #2	$89.70	9.831%	$98.5184	$98.52	$98.50	$98.50
Purchase #3	$207.66	3.612%	$215.1607	$215.16	$215.15	$215.20
Purchase #4	$134.46	8.456%	$145.8299	$145.83	$145.85	$145.80
Purchase #5	$99.72	12.155%	$111.841	$111.84	$111.85	$111.80
Purchase #6	$207.27	7.855%	$223.5511	$223.55	$223.55	$223.60
Purchase #7	$138.34	3.694%	$143.4503	$143.45	$143.45	$143.50
7 purchase totals =	$883.94		$945.3848	$945.38	$945.40	$945.40