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	$54.78	8.839%	$59.622	$59.62	$59.60	$59.60
Purchase #2	$136.67	3.688%	$141.7104	$141.71	$141.70	$141.70
Purchase #3	$183.72	12.557%	$206.7897	$206.79	$206.80	$206.80
Purchase #4	$96.54	13.603%	$109.6723	$109.67	$109.65	$109.70
Purchase #5	$68.63	3.816%	$71.2489	$71.25	$71.25	$71.20
Purchase #6	$70.39	5.145%	$74.0116	$74.01	$74.00	$74.00
Purchase #7	$181.25	10.654%	$200.5604	$200.56	$200.55	$200.60
7 purchase totals =	$791.98		$863.6153	$863.61	$863.55	$863.60