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	$148.56	6.367%	$158.0188	$158.02	$158.00	$158.00
Purchase #2	$232.87	9.561%	$255.1347	$255.13	$255.15	$255.10
Purchase #3	$47.72	9.525%	$52.2653	$52.27	$52.25	$52.30
Purchase #4	$60.83	6.619%	$64.8563	$64.86	$64.85	$64.90
Purchase #5	$213.58	12.132%	$239.4915	$239.49	$239.50	$239.50
Purchase #6	$132.33	10.200%	$145.8277	$145.83	$145.85	$145.80
Purchase #7	$223.36	12.283%	$250.7953	$250.80	$250.80	$250.80
7 purchase totals =	$1,059.25		$1,166.3896	$1,166.40	$1,166.40	$1,166.40