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	$82.73	8.328%	$89.6198	$89.62	$89.60	$89.60
Purchase #2	$63.71	13.248%	$72.1503	$72.15	$72.15	$72.20
Purchase #3	$225.83	9.705%	$247.7468	$247.75	$247.75	$247.70
Purchase #4	$130.73	8.543%	$141.8983	$141.90	$141.90	$141.90
Purchase #5	$12.90	12.325%	$14.4899	$14.49	$14.50	$14.50
Purchase #6	$101.41	9.347%	$110.8888	$110.89	$110.90	$110.90
Purchase #7	$80.35	10.564%	$88.8382	$88.84	$88.85	$88.80
7 purchase totals =	$697.66		$765.6321	$765.64	$765.65	$765.60