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	$80.69	11.701%	$90.1315	$90.13	$90.15	$90.10
Purchase #2	$228.86	7.673%	$246.4204	$246.42	$246.40	$246.40
Purchase #3	$77.90	13.628%	$88.5162	$88.52	$88.50	$88.50
Purchase #4	$169.89	12.598%	$191.2927	$191.29	$191.30	$191.30
Purchase #5	$53.72	12.551%	$60.4624	$60.46	$60.45	$60.50
Purchase #6	$240.99	6.682%	$257.093	$257.09	$257.10	$257.10
Purchase #7	$223.77	9.267%	$244.5068	$244.51	$244.50	$244.50
7 purchase totals =	$1,075.82		$1,178.4230	$1,178.42	$1,178.40	$1,178.40