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	$32.90	10.588%	$36.3835	$36.38	$36.40	$36.40
Purchase #2	$50.81	7.816%	$54.7813	$54.78	$54.80	$54.80
Purchase #3	$143.49	4.601%	$150.092	$150.09	$150.10	$150.10
Purchase #4	$69.70	3.792%	$72.343	$72.34	$72.35	$72.30
Purchase #5	$38.57	11.836%	$43.1351	$43.14	$43.15	$43.10
Purchase #6	$89.49	12.578%	$100.7461	$100.75	$100.75	$100.70
Purchase #7	$56.42	9.663%	$61.8719	$61.87	$61.85	$61.90
7 purchase totals =	$481.38		$519.3529	$519.35	$519.40	$519.30