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	$211.37	10.655%	$233.8915	$233.89	$233.90	$233.90
Purchase #2	$220.78	9.287%	$241.2838	$241.28	$241.30	$241.30
Purchase #3	$131.89	5.250%	$138.8142	$138.81	$138.80	$138.80
Purchase #4	$28.73	10.299%	$31.6889	$31.69	$31.70	$31.70
Purchase #5	$60.68	9.561%	$66.4816	$66.48	$66.50	$66.50
Purchase #6	$120.90	10.621%	$133.7408	$133.74	$133.75	$133.70
Purchase #7	$63.30	13.128%	$71.61	$71.61	$71.60	$71.60
7 purchase totals =	$837.65		$917.5108	$917.50	$917.55	$917.50