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	$55.66	12.493%	$62.6136	$62.61	$62.60	$62.60
Purchase #2	$193.66	11.547%	$216.0219	$216.02	$216.00	$216.00
Purchase #3	$37.40	9.103%	$40.8045	$40.80	$40.80	$40.80
Purchase #4	$55.48	6.829%	$59.2687	$59.27	$59.25	$59.30
Purchase #5	$47.41	8.736%	$51.5517	$51.55	$51.55	$51.60
Purchase #6	$16.91	9.115%	$18.4513	$18.45	$18.45	$18.50
Purchase #7	$88.25	7.465%	$94.8379	$94.84	$94.85	$94.80
7 purchase totals =	$494.77		$543.5496	$543.54	$543.50	$543.60