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	$67.28	6.533%	$71.6754	$71.68	$71.70	$71.70
Purchase #2	$124.74	9.716%	$136.8597	$136.86	$136.85	$136.90
Purchase #3	$200.45	6.254%	$212.9861	$212.99	$213.00	$213.00
Purchase #4	$99.71	5.341%	$105.0355	$105.04	$105.05	$105.00
Purchase #5	$75.25	4.637%	$78.7393	$78.74	$78.75	$78.70
Purchase #6	$107.61	9.789%	$118.1439	$118.14	$118.15	$118.10
Purchase #7	$167.85	10.710%	$185.8267	$185.83	$185.85	$185.80
7 purchase totals =	$842.89		$909.2666	$909.28	$909.35	$909.20