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	$167.28	13.123%	$189.2322	$189.23	$189.25	$189.20
Purchase #2	$56.32	11.506%	$62.8002	$62.80	$62.80	$62.80
Purchase #3	$175.31	8.150%	$189.5978	$189.60	$189.60	$189.60
Purchase #4	$20.83	5.799%	$22.0379	$22.04	$22.05	$22.00
Purchase #5	$69.58	3.177%	$71.7906	$71.79	$71.80	$71.80
Purchase #6	$185.68	5.853%	$196.5479	$196.55	$196.55	$196.50
Purchase #7	$191.76	13.404%	$217.4635	$217.46	$217.45	$217.50
7 purchase totals =	$866.76		$949.4701	$949.47	$949.50	$949.40