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	$103.79	13.863%	$118.1784	$118.18	$118.20	$118.20
Purchase #2	$53.84	5.661%	$56.8879	$56.89	$56.90	$56.90
Purchase #3	$55.73	9.798%	$61.1904	$61.19	$61.20	$61.20
Purchase #4	$154.96	7.302%	$166.2752	$166.28	$166.30	$166.30
Purchase #5	$91.33	3.315%	$94.3576	$94.36	$94.35	$94.40
Purchase #6	$221.25	8.669%	$240.4302	$240.43	$240.45	$240.40
Purchase #7	$213.77	12.825%	$241.186	$241.19	$241.20	$241.20
7 purchase totals =	$894.67		$978.5057	$978.52	$978.60	$978.60