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	$242.83	12.128%	$272.2804	$272.28	$272.30	$272.30
Purchase #2	$81.55	10.426%	$90.0524	$90.05	$90.05	$90.10
Purchase #3	$77.86	10.236%	$85.8297	$85.83	$85.85	$85.80
Purchase #4	$180.91	8.260%	$195.8532	$195.85	$195.85	$195.90
Purchase #5	$160.58	7.567%	$172.7311	$172.73	$172.75	$172.70
Purchase #6	$53.79	12.690%	$60.616	$60.62	$60.60	$60.60
Purchase #7	$120.91	12.681%	$136.2426	$136.24	$136.25	$136.20
7 purchase totals =	$918.43		$1,013.6054	$1,013.60	$1,013.65	$1,013.60