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	$138.68	3.195%	$143.1108	$143.11	$143.10	$143.10
Purchase #2	$158.92	12.135%	$178.2049	$178.20	$178.20	$178.20
Purchase #3	$84.43	12.636%	$95.0986	$95.10	$95.10	$95.10
Purchase #4	$86.47	9.430%	$94.6241	$94.62	$94.60	$94.60
Purchase #5	$51.61	7.355%	$55.4059	$55.41	$55.40	$55.40
Purchase #6	$50.88	4.444%	$53.1411	$53.14	$53.15	$53.10
Purchase #7	$44.32	3.245%	$45.7582	$45.76	$45.75	$45.80
7 purchase totals =	$615.31		$665.3436	$665.34	$665.30	$665.30