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	$49.80	11.333%	$55.4438	$55.44	$55.45	$55.40
Purchase #2	$71.86	7.873%	$77.5175	$77.52	$77.50	$77.50
Purchase #3	$25.37	6.689%	$27.067	$27.07	$27.05	$27.10
Purchase #4	$137.38	6.595%	$146.4402	$146.44	$146.45	$146.40
Purchase #5	$68.75	5.224%	$72.3415	$72.34	$72.35	$72.30
Purchase #6	$20.40	9.729%	$22.3847	$22.38	$22.40	$22.40
Purchase #7	$123.37	12.821%	$139.1873	$139.19	$139.20	$139.20
7 purchase totals =	$496.93		$540.3820	$540.38	$540.40	$540.30