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	$139.77	11.518%	$155.8687	$155.87	$155.85	$155.90
Purchase #2	$99.34	10.316%	$109.5879	$109.59	$109.60	$109.60
Purchase #3	$108.80	4.223%	$113.3946	$113.39	$113.40	$113.40
Purchase #4	$242.57	11.731%	$271.0259	$271.03	$271.05	$271.00
Purchase #5	$196.49	7.221%	$210.6785	$210.68	$210.70	$210.70
Purchase #6	$131.86	7.834%	$142.1899	$142.19	$142.20	$142.20
Purchase #7	$72.33	9.532%	$79.2245	$79.22	$79.20	$79.20
7 purchase totals =	$991.16		$1,081.9700	$1,081.97	$1,082.00	$1,082.00