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	$169.96	9.373%	$185.8904	$185.89	$185.90	$185.90
Purchase #2	$120.83	11.701%	$134.9683	$134.97	$134.95	$135.00
Purchase #3	$218.89	5.247%	$230.3752	$230.38	$230.40	$230.40
Purchase #4	$117.64	12.162%	$131.9474	$131.95	$131.95	$131.90
Purchase #5	$44.46	3.281%	$45.9187	$45.92	$45.90	$45.90
Purchase #6	$59.27	3.603%	$61.4055	$61.41	$61.40	$61.40
Purchase #7	$188.68	4.591%	$197.3423	$197.34	$197.35	$197.30
7 purchase totals =	$919.73		$987.8478	$987.86	$987.85	$987.80