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	$91.71	12.873%	$103.5158	$103.52	$103.50	$103.50
Purchase #2	$83.60	10.451%	$92.337	$92.34	$92.35	$92.30
Purchase #3	$69.55	5.247%	$73.1993	$73.20	$73.20	$73.20
Purchase #4	$28.48	5.714%	$30.1073	$30.11	$30.10	$30.10
Purchase #5	$175.37	9.203%	$191.5093	$191.51	$191.50	$191.50
Purchase #6	$89.50	12.189%	$100.4092	$100.41	$100.40	$100.40
Purchase #7	$108.85	11.391%	$121.2491	$121.25	$121.25	$121.20
7 purchase totals =	$647.06		$712.3270	$712.34	$712.30	$712.20