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	$116.35	6.656%	$124.0943	$124.09	$124.10	$124.10
Purchase #2	$55.96	9.748%	$61.415	$61.42	$61.40	$61.40
Purchase #3	$128.65	12.107%	$144.2257	$144.23	$144.25	$144.20
Purchase #4	$37.34	7.766%	$40.2398	$40.24	$40.25	$40.20
Purchase #5	$49.51	3.457%	$51.2216	$51.22	$51.20	$51.20
Purchase #6	$35.83	13.162%	$40.5459	$40.55	$40.55	$40.50
Purchase #7	$80.61	6.134%	$85.5546	$85.55	$85.55	$85.60
7 purchase totals =	$504.25		$547.2969	$547.30	$547.30	$547.20