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	$97.71	9.158%	$106.6583	$106.66	$106.65	$106.70
Purchase #2	$45.27	11.408%	$50.4344	$50.43	$50.45	$50.40
Purchase #3	$94.37	12.732%	$106.3852	$106.39	$106.40	$106.40
Purchase #4	$57.32	4.297%	$59.783	$59.78	$59.80	$59.80
Purchase #5	$100.42	7.422%	$107.8732	$107.87	$107.85	$107.90
Purchase #6	$75.47	6.636%	$80.4782	$80.48	$80.50	$80.50
Purchase #7	$35.41	4.169%	$36.8862	$36.89	$36.90	$36.90
7 purchase totals =	$505.97		$548.4985	$548.50	$548.55	$548.60