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	$147.72	12.103%	$165.5986	$165.60	$165.60	$165.60
Purchase #2	$42.88	10.870%	$47.5411	$47.54	$47.55	$47.50
Purchase #3	$51.83	7.499%	$55.7167	$55.72	$55.70	$55.70
Purchase #4	$84.56	7.286%	$90.721	$90.72	$90.70	$90.70
Purchase #5	$106.74	5.808%	$112.9395	$112.94	$112.95	$112.90
Purchase #6	$85.39	8.526%	$92.6704	$92.67	$92.65	$92.70
Purchase #7	$96.56	9.865%	$106.0856	$106.09	$106.10	$106.10
7 purchase totals =	$615.68		$671.2729	$671.28	$671.25	$671.20