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	$91.25	10.453%	$100.7884	$100.79	$100.80	$100.80
Purchase #2	$196.33	9.797%	$215.5645	$215.56	$215.55	$215.60
Purchase #3	$46.73	8.284%	$50.6011	$50.60	$50.60	$50.60
Purchase #4	$6.92	13.745%	$7.8712	$7.87	$7.85	$7.90
Purchase #5	$78.34	8.715%	$85.1673	$85.17	$85.15	$85.20
Purchase #6	$217.36	7.551%	$233.7729	$233.77	$233.75	$233.80
Purchase #7	$40.55	9.324%	$44.3309	$44.33	$44.35	$44.30
7 purchase totals =	$677.48		$738.0963	$738.09	$738.05	$738.20