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	$79.61	3.529%	$82.4194	$82.42	$82.40	$82.40
Purchase #2	$53.59	10.663%	$59.3043	$59.30	$59.30	$59.30
Purchase #3	$193.95	6.626%	$206.8011	$206.80	$206.80	$206.80
Purchase #4	$231.57	4.270%	$241.458	$241.46	$241.45	$241.50
Purchase #5	$141.92	11.533%	$158.2876	$158.29	$158.30	$158.30
Purchase #6	$34.54	11.221%	$38.4157	$38.42	$38.40	$38.40
Purchase #7	$109.43	11.175%	$121.6588	$121.66	$121.65	$121.70
7 purchase totals =	$844.61		$908.3449	$908.35	$908.30	$908.40