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	$57.33	4.323%	$59.8084	$59.81	$59.80	$59.80
Purchase #2	$55.86	4.689%	$58.4793	$58.48	$58.50	$58.50
Purchase #3	$101.75	3.213%	$105.0192	$105.02	$105.00	$105.00
Purchase #4	$38.42	8.452%	$41.6673	$41.67	$41.65	$41.70
Purchase #5	$46.60	5.740%	$49.2748	$49.27	$49.25	$49.30
Purchase #6	$247.89	6.552%	$264.1318	$264.13	$264.15	$264.10
Purchase #7	$129.32	9.614%	$141.7528	$141.75	$141.75	$141.80
7 purchase totals =	$677.17		$720.1336	$720.13	$720.10	$720.20