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	$67.90	6.233%	$72.1322	$72.13	$72.15	$72.10
Purchase #2	$214.88	8.471%	$233.0825	$233.08	$233.10	$233.10
Purchase #3	$16.97	9.802%	$18.6334	$18.63	$18.65	$18.60
Purchase #4	$222.51	12.823%	$251.0425	$251.04	$251.05	$251.00
Purchase #5	$38.44	12.586%	$43.2781	$43.28	$43.30	$43.30
Purchase #6	$135.78	5.252%	$142.9112	$142.91	$142.90	$142.90
Purchase #7	$124.76	13.569%	$141.6887	$141.69	$141.70	$141.70
7 purchase totals =	$821.24		$902.7686	$902.76	$902.85	$902.70