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	$69.32	13.314%	$78.5493	$78.55	$78.55	$78.50
Purchase #2	$189.98	12.490%	$213.7085	$213.71	$213.70	$213.70
Purchase #3	$189.43	10.469%	$209.2614	$209.26	$209.25	$209.30
Purchase #4	$89.65	11.596%	$100.0458	$100.05	$100.05	$100.00
Purchase #5	$75.52	4.238%	$78.7205	$78.72	$78.70	$78.70
Purchase #6	$21.72	13.501%	$24.6524	$24.65	$24.65	$24.70
Purchase #7	$69.56	13.640%	$79.048	$79.05	$79.05	$79.00
7 purchase totals =	$705.18		$783.9859	$783.99	$783.95	$783.90