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	$127.43	12.565%	$143.4416	$143.44	$143.45	$143.40
Purchase #2	$18.80	12.397%	$21.1306	$21.13	$21.15	$21.10
Purchase #3	$203.34	9.390%	$222.4336	$222.43	$222.45	$222.40
Purchase #4	$66.78	3.459%	$69.0899	$69.09	$69.10	$69.10
Purchase #5	$36.26	13.789%	$41.2599	$41.26	$41.25	$41.30
Purchase #6	$223.70	11.802%	$250.1011	$250.10	$250.10	$250.10
Purchase #7	$220.92	5.497%	$233.064	$233.06	$233.05	$233.10
7 purchase totals =	$897.23		$980.5207	$980.51	$980.55	$980.50