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	$145.25	9.375%	$158.8672	$158.87	$158.85	$158.90
Purchase #2	$99.52	13.250%	$112.7064	$112.71	$112.70	$112.70
Purchase #3	$240.88	10.629%	$266.4831	$266.48	$266.50	$266.50
Purchase #4	$11.52	10.673%	$12.7495	$12.75	$12.75	$12.70
Purchase #5	$191.61	10.501%	$211.731	$211.73	$211.75	$211.70
Purchase #6	$158.55	4.340%	$165.4311	$165.43	$165.45	$165.40
Purchase #7	$39.99	6.359%	$42.533	$42.53	$42.55	$42.50
7 purchase totals =	$887.32		$970.5013	$970.50	$970.55	$970.40