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	$108.29	9.239%	$118.2949	$118.29	$118.30	$118.30
Purchase #2	$54.64	3.193%	$56.3847	$56.38	$56.40	$56.40
Purchase #3	$41.76	9.350%	$45.6646	$45.66	$45.65	$45.70
Purchase #4	$246.47	6.244%	$261.8596	$261.86	$261.85	$261.90
Purchase #5	$53.86	10.551%	$59.5428	$59.54	$59.55	$59.50
Purchase #6	$234.43	6.166%	$248.885	$248.89	$248.90	$248.90
Purchase #7	$16.63	7.132%	$17.8161	$17.82	$17.80	$17.80
7 purchase totals =	$756.08		$808.4477	$808.44	$808.45	$808.50