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	$240.61	4.584%	$251.6396	$251.64	$251.65	$251.60
Purchase #2	$35.29	11.283%	$39.2718	$39.27	$39.25	$39.30
Purchase #3	$165.89	3.770%	$172.1441	$172.14	$172.15	$172.10
Purchase #4	$49.37	4.267%	$51.4766	$51.48	$51.50	$51.50
Purchase #5	$26.82	12.351%	$30.1325	$30.13	$30.15	$30.10
Purchase #6	$148.27	10.505%	$163.8458	$163.85	$163.85	$163.80
Purchase #7	$99.42	12.581%	$111.928	$111.93	$111.95	$111.90
7 purchase totals =	$765.67		$820.4384	$820.44	$820.50	$820.30