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	$144.45	6.238%	$153.4608	$153.46	$153.45	$153.50
Purchase #2	$35.46	12.225%	$39.795	$39.80	$39.80	$39.80
Purchase #3	$82.64	12.355%	$92.8502	$92.85	$92.85	$92.90
Purchase #4	$50.30	3.335%	$51.9775	$51.98	$52.00	$52.00
Purchase #5	$159.30	11.840%	$178.1611	$178.16	$178.15	$178.20
Purchase #6	$182.71	4.380%	$190.7127	$190.71	$190.70	$190.70
Purchase #7	$174.61	3.454%	$180.641	$180.64	$180.65	$180.60
7 purchase totals =	$829.47		$887.5983	$887.60	$887.60	$887.70