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	$131.35	3.786%	$136.3229	$136.32	$136.30	$136.30
Purchase #2	$153.48	9.580%	$168.1834	$168.18	$168.20	$168.20
Purchase #3	$79.92	7.758%	$86.1202	$86.12	$86.10	$86.10
Purchase #4	$94.58	3.243%	$97.6472	$97.65	$97.65	$97.60
Purchase #5	$21.61	13.654%	$24.5606	$24.56	$24.55	$24.60
Purchase #6	$112.97	9.399%	$123.5881	$123.59	$123.60	$123.60
Purchase #7	$78.60	5.359%	$82.8122	$82.81	$82.80	$82.80
7 purchase totals =	$672.51		$719.2346	$719.23	$719.20	$719.20