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	$69.49	11.501%	$77.482	$77.48	$77.50	$77.50
Purchase #2	$81.95	10.348%	$90.4302	$90.43	$90.45	$90.40
Purchase #3	$156.27	7.539%	$168.0512	$168.05	$168.05	$168.10
Purchase #4	$123.79	4.660%	$129.5586	$129.56	$129.55	$129.60
Purchase #5	$81.80	9.430%	$89.5137	$89.51	$89.50	$89.50
Purchase #6	$220.84	4.305%	$230.3472	$230.35	$230.35	$230.30
Purchase #7	$246.67	11.211%	$274.3242	$274.32	$274.30	$274.30
7 purchase totals =	$980.81		$1,059.7071	$1,059.70	$1,059.70	$1,059.70