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	$80.74	11.476%	$90.0057	$90.01	$90.00	$90.00
Purchase #2	$160.39	5.857%	$169.784	$169.78	$169.80	$169.80
Purchase #3	$208.43	3.748%	$216.242	$216.24	$216.25	$216.20
Purchase #4	$204.80	9.404%	$224.0594	$224.06	$224.05	$224.10
Purchase #5	$127.99	10.314%	$141.1909	$141.19	$141.20	$141.20
Purchase #6	$48.75	7.543%	$52.4272	$52.43	$52.45	$52.40
Purchase #7	$185.55	3.122%	$191.3429	$191.34	$191.35	$191.30
7 purchase totals =	$1,016.65		$1,085.0521	$1,085.05	$1,085.10	$1,085.00