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	$115.83	9.757%	$127.1315	$127.13	$127.15	$127.10
Purchase #2	$120.99	10.183%	$133.3104	$133.31	$133.30	$133.30
Purchase #3	$150.50	4.744%	$157.6397	$157.64	$157.65	$157.60
Purchase #4	$33.93	10.547%	$37.5086	$37.51	$37.50	$37.50
Purchase #5	$58.73	13.282%	$66.5305	$66.53	$66.55	$66.50
Purchase #6	$28.59	13.825%	$32.5426	$32.54	$32.55	$32.50
Purchase #7	$49.54	11.144%	$55.0607	$55.06	$55.05	$55.10
7 purchase totals =	$558.11		$609.7240	$609.72	$609.75	$609.60