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	$222.27	7.140%	$238.1401	$238.14	$238.15	$238.10
Purchase #2	$124.45	13.306%	$141.0093	$141.01	$141.00	$141.00
Purchase #3	$50.30	12.587%	$56.6313	$56.63	$56.65	$56.60
Purchase #4	$12.25	12.659%	$13.8007	$13.80	$13.80	$13.80
Purchase #5	$36.86	9.786%	$40.4671	$40.47	$40.45	$40.50
Purchase #6	$58.78	6.505%	$62.6036	$62.60	$62.60	$62.60
Purchase #7	$247.90	11.723%	$276.9613	$276.96	$276.95	$277.00
7 purchase totals =	$752.81		$829.6134	$829.61	$829.60	$829.60