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	$63.48	13.441%	$72.0123	$72.01	$72.00	$72.00
Purchase #2	$77.31	7.142%	$82.8315	$82.83	$82.85	$82.80
Purchase #3	$132.91	7.784%	$143.2557	$143.26	$143.25	$143.30
Purchase #4	$46.76	11.422%	$52.1009	$52.10	$52.10	$52.10
Purchase #5	$141.94	12.837%	$160.1608	$160.16	$160.15	$160.20
Purchase #6	$16.65	12.354%	$18.7069	$18.71	$18.70	$18.70
Purchase #7	$49.55	12.648%	$55.8171	$55.82	$55.80	$55.80
7 purchase totals =	$528.60		$584.8852	$584.89	$584.85	$584.90