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	$52.51	9.168%	$57.3241	$57.32	$57.30	$57.30
Purchase #2	$111.33	10.811%	$123.3659	$123.37	$123.35	$123.40
Purchase #3	$106.34	8.220%	$115.0811	$115.08	$115.10	$115.10
Purchase #4	$9.88	4.368%	$10.3116	$10.31	$10.30	$10.30
Purchase #5	$111.77	7.646%	$120.3159	$120.32	$120.30	$120.30
Purchase #6	$53.46	7.564%	$57.5037	$57.50	$57.50	$57.50
Purchase #7	$26.60	11.188%	$29.576	$29.58	$29.60	$29.60
7 purchase totals =	$471.89		$513.4783	$513.48	$513.45	$513.50