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	$19.82	4.366%	$20.6853	$20.69	$20.70	$20.70
Purchase #2	$37.52	5.107%	$39.4361	$39.44	$39.45	$39.40
Purchase #3	$211.68	9.381%	$231.5377	$231.54	$231.55	$231.50
Purchase #4	$177.77	7.666%	$191.3978	$191.40	$191.40	$191.40
Purchase #5	$64.70	13.173%	$73.2229	$73.22	$73.20	$73.20
Purchase #6	$144.96	13.186%	$164.0744	$164.07	$164.05	$164.10
Purchase #7	$190.48	3.353%	$196.8668	$196.87	$196.85	$196.90
7 purchase totals =	$846.93		$917.2210	$917.23	$917.20	$917.20