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	$94.81	8.570%	$102.9352	$102.94	$102.95	$102.90
Purchase #2	$67.60	11.809%	$75.5829	$75.58	$75.60	$75.60
Purchase #3	$80.82	12.170%	$90.6558	$90.66	$90.65	$90.70
Purchase #4	$12.46	9.632%	$13.6601	$13.66	$13.65	$13.70
Purchase #5	$79.84	13.326%	$90.4795	$90.48	$90.50	$90.50
Purchase #6	$64.62	8.642%	$70.2045	$70.20	$70.20	$70.20
Purchase #7	$137.42	10.305%	$151.5811	$151.58	$151.60	$151.60
7 purchase totals =	$537.57		$595.0991	$595.10	$595.15	$595.20