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	$37.60	13.235%	$42.5764	$42.58	$42.60	$42.60
Purchase #2	$144.29	9.580%	$158.113	$158.11	$158.10	$158.10
Purchase #3	$77.99	7.631%	$83.9414	$83.94	$83.95	$83.90
Purchase #4	$240.57	11.810%	$268.9813	$268.98	$269.00	$269.00
Purchase #5	$198.73	10.511%	$219.6185	$219.62	$219.60	$219.60
Purchase #6	$13.32	11.772%	$14.888	$14.89	$14.90	$14.90
Purchase #7	$102.27	7.522%	$109.9627	$109.96	$109.95	$110.00
7 purchase totals =	$814.77		$898.0813	$898.08	$898.10	$898.10