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	$123.58	6.745%	$131.9155	$131.92	$131.90	$131.90
Purchase #2	$204.37	12.656%	$230.2351	$230.24	$230.25	$230.20
Purchase #3	$243.61	5.476%	$256.9501	$256.95	$256.95	$257.00
Purchase #4	$168.55	3.457%	$174.3768	$174.38	$174.40	$174.40
Purchase #5	$56.45	5.442%	$59.522	$59.52	$59.50	$59.50
Purchase #6	$238.95	4.453%	$249.5904	$249.59	$249.60	$249.60
Purchase #7	$129.32	12.430%	$145.3945	$145.39	$145.40	$145.40
7 purchase totals =	$1,164.83		$1,247.9844	$1,247.99	$1,248.00	$1,248.00