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	$45.64	6.276%	$48.5044	$48.50	$48.50	$48.50
Purchase #2	$218.87	6.839%	$233.8385	$233.84	$233.85	$233.80
Purchase #3	$10.93	12.822%	$12.3314	$12.33	$12.35	$12.30
Purchase #4	$241.89	3.497%	$250.3489	$250.35	$250.35	$250.30
Purchase #5	$103.84	5.738%	$109.7983	$109.80	$109.80	$109.80
Purchase #6	$149.55	11.421%	$166.6301	$166.63	$166.65	$166.60
Purchase #7	$103.70	4.741%	$108.6164	$108.62	$108.60	$108.60
7 purchase totals =	$874.42		$930.0680	$930.07	$930.10	$929.90