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	$190.38	5.430%	$200.7176	$200.72	$200.70	$200.70
Purchase #2	$232.43	9.278%	$253.9949	$253.99	$254.00	$254.00
Purchase #3	$240.29	9.623%	$263.4131	$263.41	$263.40	$263.40
Purchase #4	$33.94	12.568%	$38.2056	$38.21	$38.20	$38.20
Purchase #5	$150.68	5.197%	$158.5108	$158.51	$158.50	$158.50
Purchase #6	$38.44	9.564%	$42.1164	$42.12	$42.10	$42.10
Purchase #7	$19.89	4.847%	$20.8541	$20.85	$20.85	$20.90
7 purchase totals =	$906.05		$977.8125	$977.81	$977.75	$977.80