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	$94.37	6.113%	$100.1388	$100.14	$100.15	$100.10
Purchase #2	$215.44	7.430%	$231.4472	$231.45	$231.45	$231.40
Purchase #3	$71.74	9.215%	$78.3508	$78.35	$78.35	$78.40
Purchase #4	$149.61	10.154%	$164.8014	$164.80	$164.80	$164.80
Purchase #5	$93.70	7.683%	$100.899	$100.90	$100.90	$100.90
Purchase #6	$211.37	3.808%	$219.419	$219.42	$219.40	$219.40
Purchase #7	$13.98	13.136%	$15.8164	$15.82	$15.80	$15.80
7 purchase totals =	$850.21		$910.8726	$910.88	$910.85	$910.80