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	$64.40	12.241%	$72.2832	$72.28	$72.30	$72.30
Purchase #2	$164.31	6.120%	$174.3658	$174.37	$174.35	$174.40
Purchase #3	$249.33	6.296%	$265.0278	$265.03	$265.05	$265.00
Purchase #4	$25.69	10.727%	$28.4458	$28.45	$28.45	$28.40
Purchase #5	$27.29	5.216%	$28.7134	$28.71	$28.70	$28.70
Purchase #6	$158.35	5.783%	$167.5074	$167.51	$167.50	$167.50
Purchase #7	$40.81	8.449%	$44.258	$44.26	$44.25	$44.30
7 purchase totals =	$730.18		$780.6014	$780.61	$780.60	$780.60