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	$82.72	8.237%	$89.5336	$89.53	$89.55	$89.50
Purchase #2	$102.95	7.245%	$110.4087	$110.41	$110.40	$110.40
Purchase #3	$143.25	3.337%	$148.0303	$148.03	$148.05	$148.00
Purchase #4	$40.37	13.436%	$45.7941	$45.79	$45.80	$45.80
Purchase #5	$104.95	5.417%	$110.6351	$110.64	$110.65	$110.60
Purchase #6	$5.61	12.842%	$6.3304	$6.33	$6.35	$6.30
Purchase #7	$116.41	9.753%	$127.7635	$127.76	$127.75	$127.80
7 purchase totals =	$596.26		$638.4957	$638.49	$638.55	$638.40