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	$170.33	3.107%	$175.6222	$175.62	$175.60	$175.60
Purchase #2	$90.27	8.833%	$98.2435	$98.24	$98.25	$98.20
Purchase #3	$146.44	5.233%	$154.1032	$154.10	$154.10	$154.10
Purchase #4	$77.47	10.750%	$85.798	$85.80	$85.80	$85.80
Purchase #5	$158.48	13.533%	$179.9271	$179.93	$179.95	$179.90
Purchase #6	$201.93	5.187%	$212.4041	$212.40	$212.40	$212.40
Purchase #7	$98.84	12.366%	$111.0626	$111.06	$111.05	$111.10
7 purchase totals =	$943.76		$1,017.1607	$1,017.15	$1,017.15	$1,017.10