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	$233.58	13.182%	$264.3705	$264.37	$264.35	$264.40
Purchase #2	$41.37	10.293%	$45.6282	$45.63	$45.65	$45.60
Purchase #3	$119.63	7.432%	$128.5209	$128.52	$128.50	$128.50
Purchase #4	$160.68	3.666%	$166.5705	$166.57	$166.55	$166.60
Purchase #5	$52.71	8.398%	$57.1366	$57.14	$57.15	$57.10
Purchase #6	$117.67	4.796%	$123.3135	$123.31	$123.30	$123.30
Purchase #7	$42.43	3.147%	$43.7653	$43.77	$43.75	$43.80
7 purchase totals =	$768.07		$829.3055	$829.31	$829.25	$829.30