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	$124.63	9.357%	$136.2916	$136.29	$136.30	$136.30
Purchase #2	$136.84	10.756%	$151.5585	$151.56	$151.55	$151.60
Purchase #3	$209.72	12.293%	$235.5009	$235.50	$235.50	$235.50
Purchase #4	$69.72	12.409%	$78.3716	$78.37	$78.35	$78.40
Purchase #5	$78.85	13.621%	$89.5902	$89.59	$89.60	$89.60
Purchase #6	$46.29	5.399%	$48.7892	$48.79	$48.80	$48.80
Purchase #7	$74.32	10.811%	$82.3547	$82.35	$82.35	$82.40
7 purchase totals =	$740.37		$822.4567	$822.45	$822.45	$822.60