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	$27.97	8.849%	$30.4451	$30.45	$30.45	$30.40
Purchase #2	$29.85	13.218%	$33.7956	$33.80	$33.80	$33.80
Purchase #3	$81.65	5.166%	$85.868	$85.87	$85.85	$85.90
Purchase #4	$126.98	4.472%	$132.6585	$132.66	$132.65	$132.70
Purchase #5	$35.83	5.134%	$37.6695	$37.67	$37.65	$37.70
Purchase #6	$144.30	5.247%	$151.8714	$151.87	$151.85	$151.90
Purchase #7	$42.95	11.501%	$47.8897	$47.89	$47.90	$47.90
7 purchase totals =	$489.53		$520.1978	$520.21	$520.15	$520.30