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	$40.68	7.609%	$43.7753	$43.78	$43.80	$43.80
Purchase #2	$155.54	4.187%	$162.0525	$162.05	$162.05	$162.10
Purchase #3	$27.88	10.710%	$30.8659	$30.87	$30.85	$30.90
Purchase #4	$228.36	4.277%	$238.127	$238.13	$238.15	$238.10
Purchase #5	$90.96	10.785%	$100.77	$100.77	$100.75	$100.80
Purchase #6	$88.57	4.458%	$92.5185	$92.52	$92.50	$92.50
Purchase #7	$246.26	4.186%	$256.5684	$256.57	$256.55	$256.60
7 purchase totals =	$878.25		$924.6776	$924.69	$924.65	$924.80