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	$223.58	13.336%	$253.3966	$253.40	$253.40	$253.40
Purchase #2	$91.41	5.653%	$96.5774	$96.58	$96.60	$96.60
Purchase #3	$89.35	5.590%	$94.3447	$94.34	$94.35	$94.30
Purchase #4	$100.91	5.769%	$106.7315	$106.73	$106.75	$106.70
Purchase #5	$144.72	9.420%	$158.3526	$158.35	$158.35	$158.40
Purchase #6	$108.89	10.144%	$119.9358	$119.94	$119.95	$119.90
Purchase #7	$19.35	4.118%	$20.1468	$20.15	$20.15	$20.10
7 purchase totals =	$778.21		$849.4854	$849.49	$849.55	$849.40