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	$72.93	7.608%	$78.4785	$78.48	$78.50	$78.50
Purchase #2	$220.98	12.853%	$249.3826	$249.38	$249.40	$249.40
Purchase #3	$48.72	10.235%	$53.7065	$53.71	$53.70	$53.70
Purchase #4	$70.38	11.210%	$78.2696	$78.27	$78.25	$78.30
Purchase #5	$17.93	13.640%	$20.3757	$20.38	$20.40	$20.40
Purchase #6	$204.37	4.204%	$212.9617	$212.96	$212.95	$213.00
Purchase #7	$176.64	13.846%	$201.0976	$201.10	$201.10	$201.10
7 purchase totals =	$811.95		$894.2722	$894.28	$894.30	$894.40