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	$72.89	3.119%	$75.1634	$75.16	$75.15	$75.20
Purchase #2	$232.88	12.873%	$262.8586	$262.86	$262.85	$262.90
Purchase #3	$148.84	10.470%	$164.4235	$164.42	$164.40	$164.40
Purchase #4	$24.85	3.186%	$25.6417	$25.64	$25.65	$25.60
Purchase #5	$91.93	9.104%	$100.2993	$100.30	$100.30	$100.30
Purchase #6	$47.78	13.156%	$54.0659	$54.07	$54.05	$54.10
Purchase #7	$87.27	12.481%	$98.1622	$98.16	$98.15	$98.20
7 purchase totals =	$706.44		$780.6146	$780.61	$780.55	$780.70