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	$171.55	4.858%	$179.8839	$179.88	$179.90	$179.90
Purchase #2	$27.33	3.199%	$28.2043	$28.20	$28.20	$28.20
Purchase #3	$42.98	5.229%	$45.2274	$45.23	$45.25	$45.20
Purchase #4	$200.68	11.553%	$223.8646	$223.86	$223.85	$223.90
Purchase #5	$218.38	9.687%	$239.5345	$239.53	$239.55	$239.50
Purchase #6	$196.79	13.748%	$223.8447	$223.84	$223.85	$223.80
Purchase #7	$243.72	10.806%	$270.0564	$270.06	$270.05	$270.10
7 purchase totals =	$1,101.43		$1,210.6158	$1,210.60	$1,210.65	$1,210.60