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	$30.58	7.681%	$32.9288	$32.93	$32.95	$32.90
Purchase #2	$107.96	3.571%	$111.8153	$111.82	$111.80	$111.80
Purchase #3	$245.89	9.862%	$270.1397	$270.14	$270.15	$270.10
Purchase #4	$127.79	3.590%	$132.3777	$132.38	$132.40	$132.40
Purchase #5	$51.61	5.246%	$54.3175	$54.32	$54.30	$54.30
Purchase #6	$104.78	10.389%	$115.6656	$115.67	$115.65	$115.70
Purchase #7	$55.90	9.641%	$61.2893	$61.29	$61.30	$61.30
7 purchase totals =	$724.51		$778.5339	$778.55	$778.55	$778.50