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	$85.97	13.440%	$97.5244	$97.52	$97.50	$97.50
Purchase #2	$133.72	4.243%	$139.3937	$139.39	$139.40	$139.40
Purchase #3	$68.58	5.201%	$72.1468	$72.15	$72.15	$72.10
Purchase #4	$42.45	12.825%	$47.8942	$47.89	$47.90	$47.90
Purchase #5	$5.58	6.448%	$5.9398	$5.94	$5.95	$5.90
Purchase #6	$95.32	3.663%	$98.8116	$98.81	$98.80	$98.80
Purchase #7	$197.76	13.166%	$223.7971	$223.80	$223.80	$223.80
7 purchase totals =	$629.38		$685.5076	$685.50	$685.50	$685.40