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	$36.61	11.358%	$40.7682	$40.77	$40.75	$40.80
Purchase #2	$178.29	5.690%	$188.4347	$188.43	$188.45	$188.40
Purchase #3	$56.82	10.711%	$62.906	$62.91	$62.90	$62.90
Purchase #4	$208.50	6.235%	$221.5	$221.50	$221.50	$221.50
Purchase #5	$55.52	3.462%	$57.4421	$57.44	$57.45	$57.40
Purchase #6	$139.53	11.167%	$155.1113	$155.11	$155.10	$155.10
Purchase #7	$167.85	3.499%	$173.7231	$173.72	$173.70	$173.70
7 purchase totals =	$843.12		$899.8854	$899.88	$899.85	$899.80