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	$120.62	13.695%	$137.1389	$137.14	$137.15	$137.10
Purchase #2	$194.46	10.291%	$214.4719	$214.47	$214.45	$214.50
Purchase #3	$19.43	10.604%	$21.4904	$21.49	$21.50	$21.50
Purchase #4	$230.86	6.354%	$245.5288	$245.53	$245.55	$245.50
Purchase #5	$246.59	3.346%	$254.8409	$254.84	$254.85	$254.80
Purchase #6	$167.84	10.335%	$185.1863	$185.19	$185.20	$185.20
Purchase #7	$74.95	7.550%	$80.6087	$80.61	$80.60	$80.60
7 purchase totals =	$1,054.75		$1,139.2659	$1,139.27	$1,139.30	$1,139.20