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	$75.35	5.238%	$79.2968	$79.30	$79.30	$79.30
Purchase #2	$101.76	9.526%	$111.4537	$111.45	$111.45	$111.50
Purchase #3	$143.86	5.681%	$152.0327	$152.03	$152.05	$152.00
Purchase #4	$31.78	13.828%	$36.1745	$36.17	$36.15	$36.20
Purchase #5	$171.66	11.207%	$190.8979	$190.90	$190.90	$190.90
Purchase #6	$151.45	10.290%	$167.0342	$167.03	$167.05	$167.00
Purchase #7	$234.56	11.553%	$261.6587	$261.66	$261.65	$261.70
7 purchase totals =	$910.42		$998.5485	$998.54	$998.55	$998.60