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	$19.86	6.472%	$21.1453	$21.15	$21.15	$21.10
Purchase #2	$48.96	3.462%	$50.655	$50.66	$50.65	$50.70
Purchase #3	$97.61	13.193%	$110.4877	$110.49	$110.50	$110.50
Purchase #4	$25.48	8.470%	$27.6382	$27.64	$27.65	$27.60
Purchase #5	$212.76	7.358%	$228.4149	$228.41	$228.40	$228.40
Purchase #6	$61.54	9.474%	$67.3703	$67.37	$67.35	$67.40
Purchase #7	$102.60	8.785%	$111.6134	$111.61	$111.60	$111.60
7 purchase totals =	$568.81		$617.3248	$617.33	$617.30	$617.30