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	$141.55	5.551%	$149.4074	$149.41	$149.40	$149.40
Purchase #2	$35.85	6.760%	$38.2735	$38.27	$38.25	$38.30
Purchase #3	$103.46	12.221%	$116.1038	$116.10	$116.10	$116.10
Purchase #4	$205.61	13.800%	$233.9842	$233.98	$234.00	$234.00
Purchase #5	$198.47	13.146%	$224.5609	$224.56	$224.55	$224.60
Purchase #6	$59.35	13.742%	$67.5059	$67.51	$67.50	$67.50
Purchase #7	$128.85	13.330%	$146.0257	$146.03	$146.05	$146.00
7 purchase totals =	$873.14		$975.8614	$975.86	$975.85	$975.90