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	$37.84	13.658%	$43.0082	$43.01	$43.00	$43.00
Purchase #2	$217.91	10.371%	$240.5094	$240.51	$240.50	$240.50
Purchase #3	$72.30	13.788%	$82.2687	$82.27	$82.25	$82.30
Purchase #4	$178.51	8.490%	$193.6655	$193.67	$193.65	$193.70
Purchase #5	$43.31	3.652%	$44.8917	$44.89	$44.90	$44.90
Purchase #6	$92.26	4.242%	$96.1737	$96.17	$96.15	$96.20
Purchase #7	$234.38	6.172%	$248.8459	$248.85	$248.85	$248.80
7 purchase totals =	$876.51		$949.3631	$949.37	$949.30	$949.40