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	$79.93	13.159%	$90.448	$90.45	$90.45	$90.40
Purchase #2	$36.87	3.480%	$38.1531	$38.15	$38.15	$38.20
Purchase #3	$175.89	10.457%	$194.2828	$194.28	$194.30	$194.30
Purchase #4	$112.97	6.717%	$120.5582	$120.56	$120.55	$120.60
Purchase #5	$23.57	8.553%	$25.5859	$25.59	$25.60	$25.60
Purchase #6	$215.89	3.422%	$223.2778	$223.28	$223.30	$223.30
Purchase #7	$76.50	11.682%	$85.4367	$85.44	$85.45	$85.40
7 purchase totals =	$721.62		$777.7425	$777.75	$777.80	$777.80