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	$55.30	11.755%	$61.8005	$61.80	$61.80	$61.80
Purchase #2	$244.83	4.209%	$255.1349	$255.13	$255.15	$255.10
Purchase #3	$96.46	11.537%	$107.5886	$107.59	$107.60	$107.60
Purchase #4	$58.89	11.623%	$65.7348	$65.73	$65.75	$65.70
Purchase #5	$105.93	3.515%	$109.6534	$109.65	$109.65	$109.70
Purchase #6	$201.43	4.109%	$209.7068	$209.71	$209.70	$209.70
Purchase #7	$9.93	13.155%	$11.2363	$11.24	$11.25	$11.20
7 purchase totals =	$772.77		$820.8553	$820.85	$820.90	$820.80