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	$64.97	9.760%	$71.3111	$71.31	$71.30	$71.30
Purchase #2	$157.69	13.463%	$178.9198	$178.92	$178.90	$178.90
Purchase #3	$16.81	12.433%	$18.9	$18.90	$18.90	$18.90
Purchase #4	$105.74	8.705%	$114.9447	$114.94	$114.95	$114.90
Purchase #5	$222.27	8.595%	$241.3741	$241.37	$241.35	$241.40
Purchase #6	$171.59	4.269%	$178.9152	$178.92	$178.90	$178.90
Purchase #7	$228.52	4.770%	$239.4204	$239.42	$239.40	$239.40
7 purchase totals =	$967.59		$1,043.7853	$1,043.78	$1,043.70	$1,043.70