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	$56.87	3.755%	$59.0055	$59.01	$59.00	$59.00
Purchase #2	$195.65	7.750%	$210.8129	$210.81	$210.80	$210.80
Purchase #3	$19.71	5.322%	$20.759	$20.76	$20.75	$20.80
Purchase #4	$100.42	4.526%	$104.965	$104.97	$104.95	$105.00
Purchase #5	$177.60	6.287%	$188.7657	$188.77	$188.75	$188.80
Purchase #6	$242.97	11.786%	$271.6064	$271.61	$271.60	$271.60
Purchase #7	$60.42	7.754%	$65.105	$65.11	$65.10	$65.10
7 purchase totals =	$853.64		$921.0195	$921.04	$920.95	$921.10