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	$120.99	8.614%	$131.4121	$131.41	$131.40	$131.40
Purchase #2	$144.71	13.598%	$164.3877	$164.39	$164.40	$164.40
Purchase #3	$132.60	6.624%	$141.3834	$141.38	$141.40	$141.40
Purchase #4	$220.87	11.196%	$245.5986	$245.60	$245.60	$245.60
Purchase #5	$103.83	8.584%	$112.7428	$112.74	$112.75	$112.70
Purchase #6	$145.53	13.558%	$165.261	$165.26	$165.25	$165.30
Purchase #7	$72.30	9.614%	$79.2509	$79.25	$79.25	$79.30
7 purchase totals =	$940.83		$1,040.0365	$1,040.03	$1,040.05	$1,040.10