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	$77.72	11.646%	$86.7713	$86.77	$86.75	$86.80
Purchase #2	$176.99	4.207%	$184.436	$184.44	$184.45	$184.40
Purchase #3	$244.30	11.713%	$272.9149	$272.91	$272.90	$272.90
Purchase #4	$30.88	9.819%	$33.9121	$33.91	$33.90	$33.90
Purchase #5	$113.47	13.244%	$128.498	$128.50	$128.50	$128.50
Purchase #6	$72.39	13.763%	$82.353	$82.35	$82.35	$82.40
Purchase #7	$138.43	11.422%	$154.2415	$154.24	$154.25	$154.20
7 purchase totals =	$854.18		$943.1268	$943.12	$943.10	$943.10