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	$225.89	10.464%	$249.5271	$249.53	$249.55	$249.50
Purchase #2	$172.59	7.490%	$185.517	$185.52	$185.50	$185.50
Purchase #3	$112.94	12.813%	$127.411	$127.41	$127.40	$127.40
Purchase #4	$167.99	12.672%	$189.2777	$189.28	$189.30	$189.30
Purchase #5	$142.57	10.183%	$157.0879	$157.09	$157.10	$157.10
Purchase #6	$121.51	6.538%	$129.4543	$129.45	$129.45	$129.50
Purchase #7	$242.48	3.164%	$250.1521	$250.15	$250.15	$250.20
7 purchase totals =	$1,185.97		$1,288.4271	$1,288.43	$1,288.45	$1,288.50