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	$99.61	3.230%	$102.8274	$102.83	$102.85	$102.80
Purchase #2	$230.75	10.650%	$255.3249	$255.32	$255.30	$255.30
Purchase #3	$7.91	11.704%	$8.8358	$8.84	$8.85	$8.80
Purchase #4	$119.60	6.814%	$127.7495	$127.75	$127.75	$127.70
Purchase #5	$178.63	6.455%	$190.1606	$190.16	$190.15	$190.20
Purchase #6	$139.91	6.732%	$149.3287	$149.33	$149.35	$149.30
Purchase #7	$75.61	13.236%	$85.6177	$85.62	$85.60	$85.60
7 purchase totals =	$852.02		$919.8446	$919.85	$919.85	$919.70