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	$127.82	7.640%	$137.5854	$137.59	$137.60	$137.60
Purchase #2	$179.47	5.820%	$189.9152	$189.92	$189.90	$189.90
Purchase #3	$26.38	5.670%	$27.8757	$27.88	$27.90	$27.90
Purchase #4	$208.30	7.849%	$224.6495	$224.65	$224.65	$224.60
Purchase #5	$36.96	8.301%	$40.028	$40.03	$40.05	$40.00
Purchase #6	$121.90	4.686%	$127.6122	$127.61	$127.60	$127.60
Purchase #7	$151.28	7.230%	$162.2175	$162.22	$162.20	$162.20
7 purchase totals =	$852.11		$909.8835	$909.90	$909.90	$909.80