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	$48.99	8.520%	$53.1639	$53.16	$53.15	$53.20
Purchase #2	$13.94	8.817%	$15.1691	$15.17	$15.15	$15.20
Purchase #3	$47.81	11.756%	$53.4305	$53.43	$53.45	$53.40
Purchase #4	$136.76	11.246%	$152.14	$152.14	$152.15	$152.10
Purchase #5	$150.81	11.241%	$167.7626	$167.76	$167.75	$167.80
Purchase #6	$162.89	10.165%	$179.4478	$179.45	$179.45	$179.40
Purchase #7	$212.69	3.109%	$219.3025	$219.30	$219.30	$219.30
7 purchase totals =	$773.89		$840.4164	$840.41	$840.40	$840.40