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	$138.25	5.636%	$146.0418	$146.04	$146.05	$146.00
Purchase #2	$78.68	10.656%	$87.0641	$87.06	$87.05	$87.10
Purchase #3	$212.89	4.560%	$222.5978	$222.60	$222.60	$222.60
Purchase #4	$112.81	7.491%	$121.2606	$121.26	$121.25	$121.30
Purchase #5	$159.81	9.716%	$175.3371	$175.34	$175.35	$175.30
Purchase #6	$103.50	5.369%	$109.0569	$109.06	$109.05	$109.10
Purchase #7	$135.31	4.619%	$141.56	$141.56	$141.55	$141.60
7 purchase totals =	$941.25		$1,002.9183	$1,002.92	$1,002.90	$1,003.00