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	$71.59	3.432%	$74.047	$74.05	$74.05	$74.00
Purchase #2	$171.44	6.156%	$181.9938	$181.99	$182.00	$182.00
Purchase #3	$135.31	12.702%	$152.4971	$152.50	$152.50	$152.50
Purchase #4	$43.89	6.270%	$46.6419	$46.64	$46.65	$46.60
Purchase #5	$138.64	9.650%	$152.0188	$152.02	$152.00	$152.00
Purchase #6	$92.60	12.406%	$104.088	$104.09	$104.10	$104.10
Purchase #7	$113.41	12.412%	$127.4864	$127.49	$127.50	$127.50
7 purchase totals =	$766.88		$838.7730	$838.78	$838.80	$838.70