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	$139.76	13.186%	$158.1888	$158.19	$158.20	$158.20
Purchase #2	$65.91	9.586%	$72.2281	$72.23	$72.25	$72.20
Purchase #3	$158.70	6.206%	$168.5489	$168.55	$168.55	$168.50
Purchase #4	$36.50	5.390%	$38.4674	$38.47	$38.45	$38.50
Purchase #5	$141.94	13.383%	$160.9358	$160.94	$160.95	$160.90
Purchase #6	$58.96	5.209%	$62.0312	$62.03	$62.05	$62.00
Purchase #7	$64.54	6.325%	$68.6222	$68.62	$68.60	$68.60
7 purchase totals =	$666.31		$729.0224	$729.03	$729.05	$728.90