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	$34.85	8.383%	$37.7715	$37.77	$37.75	$37.80
Purchase #2	$144.47	7.332%	$155.0625	$155.06	$155.05	$155.10
Purchase #3	$93.39	12.495%	$105.0591	$105.06	$105.05	$105.10
Purchase #4	$151.45	4.529%	$158.3092	$158.31	$158.30	$158.30
Purchase #5	$12.36	6.238%	$13.131	$13.13	$13.15	$13.10
Purchase #6	$41.68	7.685%	$44.8831	$44.88	$44.90	$44.90
Purchase #7	$109.45	8.678%	$118.9481	$118.95	$118.95	$118.90
7 purchase totals =	$587.65		$633.1645	$633.16	$633.15	$633.20