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	$158.91	13.360%	$180.1404	$180.14	$180.15	$180.10
Purchase #2	$112.30	10.774%	$124.3992	$124.40	$124.40	$124.40
Purchase #3	$113.40	4.485%	$118.486	$118.49	$118.50	$118.50
Purchase #4	$92.56	7.618%	$99.6112	$99.61	$99.60	$99.60
Purchase #5	$101.25	10.658%	$112.0412	$112.04	$112.05	$112.00
Purchase #6	$144.28	4.567%	$150.8693	$150.87	$150.85	$150.90
Purchase #7	$249.65	5.839%	$264.2271	$264.23	$264.25	$264.20
7 purchase totals =	$972.35		$1,049.7744	$1,049.78	$1,049.80	$1,049.70