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	$23.96	13.317%	$27.1508	$27.15	$27.15	$27.20
Purchase #2	$234.29	6.823%	$250.2756	$250.28	$250.30	$250.30
Purchase #3	$230.64	10.294%	$254.3821	$254.38	$254.40	$254.40
Purchase #4	$198.72	6.712%	$212.0581	$212.06	$212.05	$212.10
Purchase #5	$195.59	6.418%	$208.143	$208.14	$208.15	$208.10
Purchase #6	$57.30	7.463%	$61.5763	$61.58	$61.60	$61.60
Purchase #7	$93.42	12.599%	$105.19	$105.19	$105.20	$105.20
7 purchase totals =	$1,033.92		$1,118.7759	$1,118.78	$1,118.85	$1,118.90