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	$19.60	5.279%	$20.6347	$20.63	$20.65	$20.60
Purchase #2	$129.57	13.815%	$147.4701	$147.47	$147.45	$147.50
Purchase #3	$104.72	6.448%	$111.4723	$111.47	$111.45	$111.50
Purchase #4	$48.36	11.168%	$53.7608	$53.76	$53.75	$53.80
Purchase #5	$46.98	10.792%	$52.0501	$52.05	$52.05	$52.10
Purchase #6	$35.33	13.731%	$40.1812	$40.18	$40.20	$40.20
Purchase #7	$204.39	12.188%	$229.3011	$229.30	$229.30	$229.30
7 purchase totals =	$588.95		$654.8703	$654.86	$654.85	$655.00