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	$7.25	11.193%	$8.0615	$8.06	$8.05	$8.10
Purchase #2	$162.51	6.343%	$172.818	$172.82	$172.80	$172.80
Purchase #3	$71.70	7.530%	$77.099	$77.10	$77.10	$77.10
Purchase #4	$140.84	13.688%	$160.1182	$160.12	$160.10	$160.10
Purchase #5	$46.56	10.236%	$51.3259	$51.33	$51.35	$51.30
Purchase #6	$59.35	8.396%	$64.333	$64.33	$64.35	$64.30
Purchase #7	$125.50	11.243%	$139.61	$139.61	$139.60	$139.60
7 purchase totals =	$613.71		$673.3656	$673.37	$673.35	$673.30