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	$52.65	13.210%	$59.6051	$59.61	$59.60	$59.60
Purchase #2	$152.27	3.649%	$157.8263	$157.83	$157.85	$157.80
Purchase #3	$169.56	11.725%	$189.4409	$189.44	$189.45	$189.40
Purchase #4	$22.41	7.757%	$24.1483	$24.15	$24.15	$24.10
Purchase #5	$99.81	10.121%	$109.9118	$109.91	$109.90	$109.90
Purchase #6	$230.34	6.396%	$245.0725	$245.07	$245.05	$245.10
Purchase #7	$189.40	10.630%	$209.5332	$209.53	$209.55	$209.50
7 purchase totals =	$916.44		$995.5381	$995.54	$995.55	$995.40