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	$80.92	13.791%	$92.0797	$92.08	$92.10	$92.10
Purchase #2	$206.73	5.810%	$218.741	$218.74	$218.75	$218.70
Purchase #3	$236.49	7.494%	$254.2126	$254.21	$254.20	$254.20
Purchase #4	$41.98	4.288%	$43.7801	$43.78	$43.80	$43.80
Purchase #5	$119.87	6.652%	$127.8438	$127.84	$127.85	$127.80
Purchase #6	$81.71	10.369%	$90.1825	$90.18	$90.20	$90.20
Purchase #7	$145.39	13.274%	$164.6891	$164.69	$164.70	$164.70
7 purchase totals =	$913.09		$991.5288	$991.52	$991.60	$991.50