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	$207.70	12.532%	$233.729	$233.73	$233.75	$233.70
Purchase #2	$106.64	4.342%	$111.2703	$111.27	$111.25	$111.30
Purchase #3	$109.81	4.625%	$114.8887	$114.89	$114.90	$114.90
Purchase #4	$72.37	4.148%	$75.3719	$75.37	$75.35	$75.40
Purchase #5	$194.64	3.159%	$200.7887	$200.79	$200.80	$200.80
Purchase #6	$115.90	12.873%	$130.8198	$130.82	$130.80	$130.80
Purchase #7	$107.71	3.779%	$111.7804	$111.78	$111.80	$111.80
7 purchase totals =	$914.77		$978.6488	$978.65	$978.65	$978.70