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	$36.54	5.572%	$38.576	$38.58	$38.60	$38.60
Purchase #2	$141.77	13.239%	$160.5389	$160.54	$160.55	$160.50
Purchase #3	$47.63	6.218%	$50.5916	$50.59	$50.60	$50.60
Purchase #4	$149.35	7.535%	$160.6035	$160.60	$160.60	$160.60
Purchase #5	$109.41	4.235%	$114.0435	$114.04	$114.05	$114.00
Purchase #6	$231.63	3.143%	$238.9101	$238.91	$238.90	$238.90
Purchase #7	$162.49	5.823%	$171.9518	$171.95	$171.95	$172.00
7 purchase totals =	$878.82		$935.2154	$935.21	$935.25	$935.20