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	$78.46	6.369%	$83.4571	$83.46	$83.45	$83.50
Purchase #2	$34.63	11.248%	$38.5252	$38.53	$38.55	$38.50
Purchase #3	$187.59	4.680%	$196.3692	$196.37	$196.35	$196.40
Purchase #4	$96.42	13.447%	$109.3856	$109.39	$109.40	$109.40
Purchase #5	$218.98	3.103%	$225.7749	$225.77	$225.75	$225.80
Purchase #6	$170.98	10.383%	$188.7329	$188.73	$188.75	$188.70
Purchase #7	$148.55	4.474%	$155.1961	$155.20	$155.20	$155.20
7 purchase totals =	$935.61		$997.4410	$997.45	$997.45	$997.50