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	$240.76	6.824%	$257.1895	$257.19	$257.20	$257.20
Purchase #2	$204.54	12.670%	$230.4552	$230.46	$230.45	$230.50
Purchase #3	$81.30	6.276%	$86.4024	$86.40	$86.40	$86.40
Purchase #4	$236.75	11.694%	$264.4355	$264.44	$264.45	$264.40
Purchase #5	$197.69	11.201%	$219.8333	$219.83	$219.85	$219.80
Purchase #6	$59.93	3.284%	$61.8981	$61.90	$61.90	$61.90
Purchase #7	$82.74	9.686%	$90.7542	$90.75	$90.75	$90.80
7 purchase totals =	$1,103.71		$1,210.9682	$1,210.97	$1,211.00	$1,211.00