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	$80.72	3.328%	$83.4064	$83.41	$83.40	$83.40
Purchase #2	$28.93	4.194%	$30.1433	$30.14	$30.15	$30.10
Purchase #3	$53.46	9.579%	$58.5809	$58.58	$58.60	$58.60
Purchase #4	$106.90	4.727%	$111.9532	$111.95	$111.95	$112.00
Purchase #5	$101.63	4.166%	$105.8639	$105.86	$105.85	$105.90
Purchase #6	$109.25	13.626%	$124.1364	$124.14	$124.15	$124.10
Purchase #7	$105.25	12.597%	$118.5083	$118.51	$118.50	$118.50
7 purchase totals =	$586.14		$632.5924	$632.59	$632.60	$632.60