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	$54.37	6.861%	$58.1003	$58.10	$58.10	$58.10
Purchase #2	$219.88	6.256%	$233.6357	$233.64	$233.65	$233.60
Purchase #3	$171.87	9.526%	$188.2423	$188.24	$188.25	$188.20
Purchase #4	$86.27	4.761%	$90.3773	$90.38	$90.40	$90.40
Purchase #5	$28.98	13.222%	$32.8117	$32.81	$32.80	$32.80
Purchase #6	$129.78	9.431%	$142.0196	$142.02	$142.00	$142.00
Purchase #7	$35.86	13.502%	$40.7018	$40.70	$40.70	$40.70
7 purchase totals =	$727.01		$785.8887	$785.89	$785.90	$785.80