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	$11.87	6.842%	$12.6821	$12.68	$12.70	$12.70
Purchase #2	$72.55	7.751%	$78.1734	$78.17	$78.15	$78.20
Purchase #3	$213.46	4.790%	$223.6847	$223.68	$223.70	$223.70
Purchase #4	$179.67	5.244%	$189.0919	$189.09	$189.10	$189.10
Purchase #5	$182.99	9.735%	$200.8041	$200.80	$200.80	$200.80
Purchase #6	$104.94	13.451%	$119.0555	$119.06	$119.05	$119.10
Purchase #7	$82.72	3.857%	$85.9105	$85.91	$85.90	$85.90
7 purchase totals =	$848.20		$909.4022	$909.39	$909.40	$909.50