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	$139.41	6.454%	$148.4075	$148.41	$148.40	$148.40
Purchase #2	$85.96	4.231%	$89.597	$89.60	$89.60	$89.60
Purchase #3	$92.39	8.185%	$99.9521	$99.95	$99.95	$100.00
Purchase #4	$164.50	9.342%	$179.8676	$179.87	$179.85	$179.90
Purchase #5	$30.98	5.581%	$32.709	$32.71	$32.70	$32.70
Purchase #6	$98.75	12.515%	$111.1086	$111.11	$111.10	$111.10
Purchase #7	$184.37	5.451%	$194.42	$194.42	$194.40	$194.40
7 purchase totals =	$796.36		$856.0618	$856.07	$856.00	$856.10