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	$89.72	11.216%	$99.783	$99.78	$99.80	$99.80
Purchase #2	$157.77	13.227%	$178.6382	$178.64	$178.65	$178.60
Purchase #3	$117.98	11.458%	$131.4981	$131.50	$131.50	$131.50
Purchase #4	$82.81	12.530%	$93.1861	$93.19	$93.20	$93.20
Purchase #5	$83.53	5.540%	$88.1576	$88.16	$88.15	$88.20
Purchase #6	$114.67	5.363%	$120.8198	$120.82	$120.80	$120.80
Purchase #7	$208.68	6.693%	$222.647	$222.65	$222.65	$222.60
7 purchase totals =	$855.16		$934.7298	$934.74	$934.75	$934.70