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	$38.39	13.265%	$43.4824	$43.48	$43.50	$43.50
Purchase #2	$92.71	6.518%	$98.7528	$98.75	$98.75	$98.80
Purchase #3	$6.70	9.326%	$7.3248	$7.32	$7.30	$7.30
Purchase #4	$172.81	4.387%	$180.3912	$180.39	$180.40	$180.40
Purchase #5	$189.96	11.735%	$212.2518	$212.25	$212.25	$212.30
Purchase #6	$53.74	5.289%	$56.5823	$56.58	$56.60	$56.60
Purchase #7	$33.89	13.613%	$38.5034	$38.50	$38.50	$38.50
7 purchase totals =	$588.20		$637.2887	$637.27	$637.30	$637.40