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	$50.56	12.424%	$56.8416	$56.84	$56.85	$56.80
Purchase #2	$148.30	12.767%	$167.2335	$167.23	$167.25	$167.20
Purchase #3	$86.36	4.532%	$90.2738	$90.27	$90.25	$90.30
Purchase #4	$73.83	10.212%	$81.3695	$81.37	$81.35	$81.40
Purchase #5	$126.97	13.309%	$143.8684	$143.87	$143.85	$143.90
Purchase #6	$184.58	8.436%	$200.1512	$200.15	$200.15	$200.20
Purchase #7	$158.72	3.528%	$164.3196	$164.32	$164.30	$164.30
7 purchase totals =	$829.32		$904.0576	$904.05	$904.00	$904.10