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	$37.81	11.248%	$42.0629	$42.06	$42.05	$42.10
Purchase #2	$102.37	5.576%	$108.0782	$108.08	$108.10	$108.10
Purchase #3	$95.41	4.485%	$99.6891	$99.69	$99.70	$99.70
Purchase #4	$218.40	13.499%	$247.8818	$247.88	$247.90	$247.90
Purchase #5	$229.45	11.406%	$255.6211	$255.62	$255.60	$255.60
Purchase #6	$219.61	5.837%	$232.4286	$232.43	$232.45	$232.40
Purchase #7	$104.89	11.623%	$117.0814	$117.08	$117.10	$117.10
7 purchase totals =	$1,007.94		$1,102.8431	$1,102.84	$1,102.90	$1,102.90