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	$49.47	12.270%	$55.54	$55.54	$55.55	$55.50
Purchase #2	$40.66	12.596%	$45.7815	$45.78	$45.80	$45.80
Purchase #3	$85.59	6.347%	$91.0224	$91.02	$91.00	$91.00
Purchase #4	$61.54	8.552%	$66.8029	$66.80	$66.80	$66.80
Purchase #5	$248.36	9.264%	$271.3681	$271.37	$271.35	$271.40
Purchase #6	$225.77	13.140%	$255.4362	$255.44	$255.45	$255.40
Purchase #7	$128.61	13.260%	$145.6637	$145.66	$145.65	$145.70
7 purchase totals =	$840.00		$931.6148	$931.61	$931.60	$931.60