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	$173.64	3.618%	$179.9223	$179.92	$179.90	$179.90
Purchase #2	$74.50	8.839%	$81.0851	$81.09	$81.10	$81.10
Purchase #3	$171.86	12.621%	$193.5505	$193.55	$193.55	$193.60
Purchase #4	$40.62	5.150%	$42.7119	$42.71	$42.70	$42.70
Purchase #5	$249.94	4.637%	$261.5297	$261.53	$261.55	$261.50
Purchase #6	$212.94	13.321%	$241.3057	$241.31	$241.30	$241.30
Purchase #7	$12.40	3.408%	$12.8226	$12.82	$12.80	$12.80
7 purchase totals =	$935.90		$1,012.9278	$1,012.93	$1,012.90	$1,012.90