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	$31.90	5.293%	$33.5885	$33.59	$33.60	$33.60
Purchase #2	$249.93	10.123%	$275.2304	$275.23	$275.25	$275.20
Purchase #3	$182.69	4.411%	$190.7485	$190.75	$190.75	$190.70
Purchase #4	$60.55	13.160%	$68.5184	$68.52	$68.50	$68.50
Purchase #5	$25.44	6.808%	$27.172	$27.17	$27.15	$27.20
Purchase #6	$59.99	8.506%	$65.0927	$65.09	$65.10	$65.10
Purchase #7	$185.91	13.219%	$210.4854	$210.49	$210.50	$210.50
7 purchase totals =	$796.41		$870.8359	$870.84	$870.85	$870.80