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	$20.30	9.525%	$22.2336	$22.23	$22.25	$22.20
Purchase #2	$183.69	9.200%	$200.5895	$200.59	$200.60	$200.60
Purchase #3	$20.39	6.382%	$21.6913	$21.69	$21.70	$21.70
Purchase #4	$25.73	10.708%	$28.4852	$28.49	$28.50	$28.50
Purchase #5	$81.84	12.203%	$91.8269	$91.83	$91.85	$91.80
Purchase #6	$39.73	9.349%	$43.4444	$43.44	$43.45	$43.40
Purchase #7	$85.56	5.769%	$90.496	$90.50	$90.50	$90.50
7 purchase totals =	$457.24		$498.7669	$498.77	$498.85	$498.70