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	$177.59	3.833%	$184.397	$184.40	$184.40	$184.40
Purchase #2	$226.71	12.642%	$255.3707	$255.37	$255.35	$255.40
Purchase #3	$120.73	6.414%	$128.4736	$128.47	$128.45	$128.50
Purchase #4	$171.83	11.330%	$191.2983	$191.30	$191.30	$191.30
Purchase #5	$69.89	13.735%	$79.4894	$79.49	$79.50	$79.50
Purchase #6	$57.91	4.434%	$60.4777	$60.48	$60.50	$60.50
Purchase #7	$122.30	7.159%	$131.0555	$131.06	$131.05	$131.10
7 purchase totals =	$946.96		$1,030.5622	$1,030.57	$1,030.55	$1,030.70