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	$42.74	11.751%	$47.7624	$47.76	$47.75	$47.80
Purchase #2	$51.42	10.302%	$56.7173	$56.72	$56.70	$56.70
Purchase #3	$44.29	7.230%	$47.4922	$47.49	$47.50	$47.50
Purchase #4	$142.78	5.141%	$150.1203	$150.12	$150.10	$150.10
Purchase #5	$155.84	8.494%	$169.077	$169.08	$169.10	$169.10
Purchase #6	$143.85	10.404%	$158.8162	$158.82	$158.80	$158.80
Purchase #7	$42.54	10.863%	$47.1611	$47.16	$47.15	$47.20
7 purchase totals =	$623.46		$677.1465	$677.15	$677.10	$677.20