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	$40.40	7.248%	$43.3282	$43.33	$43.35	$43.30
Purchase #2	$137.96	8.828%	$150.1391	$150.14	$150.15	$150.10
Purchase #3	$29.99	8.490%	$32.5362	$32.54	$32.55	$32.50
Purchase #4	$166.57	11.678%	$186.022	$186.02	$186.00	$186.00
Purchase #5	$33.98	8.640%	$36.9159	$36.92	$36.90	$36.90
Purchase #6	$41.33	9.697%	$45.3378	$45.34	$45.35	$45.30
Purchase #7	$121.81	10.650%	$134.7828	$134.78	$134.80	$134.80
7 purchase totals =	$572.04		$629.0620	$629.07	$629.10	$628.90