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	$73.90	5.843%	$78.218	$78.22	$78.20	$78.20
Purchase #2	$226.33	13.558%	$257.0158	$257.02	$257.00	$257.00
Purchase #3	$5.64	11.409%	$6.2835	$6.28	$6.30	$6.30
Purchase #4	$144.31	4.371%	$150.6178	$150.62	$150.60	$150.60
Purchase #5	$79.31	12.723%	$89.4006	$89.40	$89.40	$89.40
Purchase #6	$60.55	5.534%	$63.9008	$63.90	$63.90	$63.90
Purchase #7	$98.84	9.807%	$108.5332	$108.53	$108.55	$108.50
7 purchase totals =	$688.88		$753.9697	$753.97	$753.95	$753.90