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	$153.47	6.139%	$162.8915	$162.89	$162.90	$162.90
Purchase #2	$203.46	12.415%	$228.7196	$228.72	$228.70	$228.70
Purchase #3	$161.60	5.845%	$171.0455	$171.05	$171.05	$171.00
Purchase #4	$98.95	7.631%	$106.5009	$106.50	$106.50	$106.50
Purchase #5	$156.78	9.325%	$171.3997	$171.40	$171.40	$171.40
Purchase #6	$240.81	4.805%	$252.3809	$252.38	$252.40	$252.40
Purchase #7	$179.77	11.565%	$200.5604	$200.56	$200.55	$200.60
7 purchase totals =	$1,194.84		$1,293.4985	$1,293.50	$1,293.50	$1,293.50