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	$48.31	5.285%	$50.8632	$50.86	$50.85	$50.90
Purchase #2	$144.80	9.502%	$158.5589	$158.56	$158.55	$158.60
Purchase #3	$130.77	7.388%	$140.4313	$140.43	$140.45	$140.40
Purchase #4	$17.96	11.828%	$20.0843	$20.08	$20.10	$20.10
Purchase #5	$90.83	3.538%	$94.0436	$94.04	$94.05	$94.00
Purchase #6	$179.79	11.820%	$201.0412	$201.04	$201.05	$201.00
Purchase #7	$116.85	13.373%	$132.4764	$132.48	$132.50	$132.50
7 purchase totals =	$729.31		$797.4989	$797.49	$797.55	$797.50