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	$39.62	7.314%	$42.5178	$42.52	$42.50	$42.50
Purchase #2	$112.78	13.713%	$128.2455	$128.25	$128.25	$128.20
Purchase #3	$115.68	4.147%	$120.4772	$120.48	$120.50	$120.50
Purchase #4	$238.98	10.464%	$263.9869	$263.99	$264.00	$264.00
Purchase #5	$210.31	7.275%	$225.6101	$225.61	$225.60	$225.60
Purchase #6	$50.66	7.645%	$54.533	$54.53	$54.55	$54.50
Purchase #7	$238.94	11.404%	$266.1887	$266.19	$266.20	$266.20
7 purchase totals =	$1,006.97		$1,101.5592	$1,101.57	$1,101.60	$1,101.50