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	$117.71	5.622%	$124.3277	$124.33	$124.35	$124.30
Purchase #2	$216.51	4.535%	$226.3287	$226.33	$226.35	$226.30
Purchase #3	$237.51	3.105%	$244.8847	$244.88	$244.90	$244.90
Purchase #4	$25.71	10.130%	$28.3144	$28.31	$28.30	$28.30
Purchase #5	$30.83	7.863%	$33.2542	$33.25	$33.25	$33.30
Purchase #6	$29.76	7.857%	$32.0982	$32.10	$32.10	$32.10
Purchase #7	$134.37	5.386%	$141.6072	$141.61	$141.60	$141.60
7 purchase totals =	$792.40		$830.8151	$830.81	$830.85	$830.80