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	$226.63	12.351%	$254.6211	$254.62	$254.60	$254.60
Purchase #2	$160.97	8.193%	$174.1583	$174.16	$174.15	$174.20
Purchase #3	$225.50	3.360%	$233.0768	$233.08	$233.10	$233.10
Purchase #4	$35.27	4.448%	$36.8388	$36.84	$36.85	$36.80
Purchase #5	$198.42	5.404%	$209.1426	$209.14	$209.15	$209.10
Purchase #6	$85.45	4.396%	$89.2064	$89.21	$89.20	$89.20
Purchase #7	$42.61	6.603%	$45.4235	$45.42	$45.40	$45.40
7 purchase totals =	$974.85		$1,042.4675	$1,042.47	$1,042.45	$1,042.40