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	$143.96	10.399%	$158.9304	$158.93	$158.95	$158.90
Purchase #2	$93.47	4.299%	$97.4883	$97.49	$97.50	$97.50
Purchase #3	$16.53	7.225%	$17.7243	$17.72	$17.70	$17.70
Purchase #4	$100.94	12.419%	$113.4757	$113.48	$113.50	$113.50
Purchase #5	$173.45	6.821%	$185.281	$185.28	$185.30	$185.30
Purchase #6	$241.69	10.177%	$266.2868	$266.29	$266.30	$266.30
Purchase #7	$69.40	13.168%	$78.5386	$78.54	$78.55	$78.50
7 purchase totals =	$839.44		$917.7251	$917.73	$917.80	$917.70