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	$247.96	11.274%	$275.915	$275.92	$275.90	$275.90
Purchase #2	$61.29	9.742%	$67.2609	$67.26	$67.25	$67.30
Purchase #3	$181.29	6.229%	$192.5826	$192.58	$192.60	$192.60
Purchase #4	$76.96	9.542%	$84.3035	$84.30	$84.30	$84.30
Purchase #5	$19.93	3.247%	$20.5771	$20.58	$20.60	$20.60
Purchase #6	$131.66	8.484%	$142.83	$142.83	$142.85	$142.80
Purchase #7	$53.66	10.679%	$59.3904	$59.39	$59.40	$59.40
7 purchase totals =	$772.75		$842.8595	$842.86	$842.90	$842.90