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	$121.92	4.476%	$127.3771	$127.38	$127.40	$127.40
Purchase #2	$71.97	6.361%	$76.548	$76.55	$76.55	$76.50
Purchase #3	$135.91	3.430%	$140.5717	$140.57	$140.55	$140.60
Purchase #4	$237.30	11.233%	$263.9559	$263.96	$263.95	$264.00
Purchase #5	$49.95	11.714%	$55.8011	$55.80	$55.80	$55.80
Purchase #6	$109.84	8.837%	$119.5466	$119.55	$119.55	$119.50
Purchase #7	$53.47	11.802%	$59.7805	$59.78	$59.80	$59.80
7 purchase totals =	$780.36		$843.5809	$843.59	$843.60	$843.60