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	$96.46	4.211%	$100.5219	$100.52	$100.50	$100.50
Purchase #2	$59.99	12.747%	$67.6369	$67.64	$67.65	$67.60
Purchase #3	$75.41	4.198%	$78.5757	$78.58	$78.60	$78.60
Purchase #4	$82.39	7.537%	$88.5997	$88.60	$88.60	$88.60
Purchase #5	$110.74	9.150%	$120.8727	$120.87	$120.85	$120.90
Purchase #6	$71.84	9.762%	$78.853	$78.85	$78.85	$78.90
Purchase #7	$71.84	13.116%	$81.2625	$81.26	$81.25	$81.30
7 purchase totals =	$568.67		$616.3224	$616.32	$616.30	$616.40