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	$84.78	5.117%	$89.1182	$89.12	$89.10	$89.10
Purchase #2	$7.81	10.786%	$8.6524	$8.65	$8.65	$8.70
Purchase #3	$120.37	8.739%	$130.8891	$130.89	$130.90	$130.90
Purchase #4	$68.94	7.861%	$74.3594	$74.36	$74.35	$74.40
Purchase #5	$171.30	6.537%	$182.4979	$182.50	$182.50	$182.50
Purchase #6	$181.98	13.678%	$206.8712	$206.87	$206.85	$206.90
Purchase #7	$112.86	13.209%	$127.7677	$127.77	$127.75	$127.80
7 purchase totals =	$748.04		$820.1559	$820.16	$820.10	$820.30