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	$135.72	5.307%	$142.9227	$142.92	$142.90	$142.90
Purchase #2	$152.58	12.680%	$171.9271	$171.93	$171.95	$171.90
Purchase #3	$227.45	12.304%	$255.4354	$255.44	$255.45	$255.40
Purchase #4	$27.45	9.866%	$30.1582	$30.16	$30.15	$30.20
Purchase #5	$151.44	7.425%	$162.6844	$162.68	$162.70	$162.70
Purchase #6	$130.58	11.667%	$145.8148	$145.81	$145.80	$145.80
Purchase #7	$245.89	12.514%	$276.6607	$276.66	$276.65	$276.70
7 purchase totals =	$1,071.11		$1,185.6033	$1,185.60	$1,185.60	$1,185.60