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	$51.90	8.411%	$56.2653	$56.27	$56.25	$56.30
Purchase #2	$45.49	4.501%	$47.5375	$47.54	$47.55	$47.50
Purchase #3	$13.38	8.734%	$14.5486	$14.55	$14.55	$14.50
Purchase #4	$6.46	9.258%	$7.0581	$7.06	$7.05	$7.10
Purchase #5	$236.48	8.180%	$255.8241	$255.82	$255.80	$255.80
Purchase #6	$82.51	11.117%	$91.6826	$91.68	$91.70	$91.70
Purchase #7	$99.67	12.254%	$111.8836	$111.88	$111.90	$111.90
7 purchase totals =	$535.89		$584.7998	$584.80	$584.80	$584.80