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	$43.99	12.210%	$49.3612	$49.36	$49.35	$49.40
Purchase #2	$163.52	12.213%	$183.4907	$183.49	$183.50	$183.50
Purchase #3	$124.92	4.116%	$130.0617	$130.06	$130.05	$130.10
Purchase #4	$237.89	7.705%	$256.2194	$256.22	$256.20	$256.20
Purchase #5	$82.83	3.309%	$85.5708	$85.57	$85.55	$85.60
Purchase #6	$41.34	10.164%	$45.5418	$45.54	$45.55	$45.50
Purchase #7	$36.59	4.413%	$38.2047	$38.20	$38.20	$38.20
7 purchase totals =	$731.08		$788.4503	$788.44	$788.40	$788.50