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	$103.27	6.831%	$110.3244	$110.32	$110.30	$110.30
Purchase #2	$53.58	11.231%	$59.5976	$59.60	$59.60	$59.60
Purchase #3	$139.92	13.279%	$158.5	$158.50	$158.50	$158.50
Purchase #4	$82.91	8.437%	$89.9051	$89.91	$89.90	$89.90
Purchase #5	$162.78	9.605%	$178.415	$178.42	$178.40	$178.40
Purchase #6	$25.76	5.331%	$27.1333	$27.13	$27.15	$27.10
Purchase #7	$110.85	4.192%	$115.4968	$115.50	$115.50	$115.50
7 purchase totals =	$679.07		$739.3722	$739.38	$739.35	$739.30