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	$80.74	7.300%	$86.634	$86.63	$86.65	$86.60
Purchase #2	$123.44	12.812%	$139.2551	$139.26	$139.25	$139.30
Purchase #3	$162.79	12.692%	$183.4513	$183.45	$183.45	$183.50
Purchase #4	$133.57	4.323%	$139.3442	$139.34	$139.35	$139.30
Purchase #5	$54.41	6.122%	$57.741	$57.74	$57.75	$57.70
Purchase #6	$250.89	8.622%	$272.5217	$272.52	$272.50	$272.50
Purchase #7	$143.82	7.737%	$154.9474	$154.95	$154.95	$154.90
7 purchase totals =	$949.66		$1,033.8947	$1,033.89	$1,033.90	$1,033.80