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	$140.86	7.639%	$151.6203	$151.62	$151.60	$151.60
Purchase #2	$125.69	10.289%	$138.6222	$138.62	$138.60	$138.60
Purchase #3	$250.75	12.260%	$281.492	$281.49	$281.50	$281.50
Purchase #4	$69.92	12.675%	$78.7824	$78.78	$78.80	$78.80
Purchase #5	$128.63	11.252%	$143.1034	$143.10	$143.10	$143.10
Purchase #6	$75.48	8.106%	$81.5984	$81.60	$81.60	$81.60
Purchase #7	$12.82	11.385%	$14.2796	$14.28	$14.30	$14.30
7 purchase totals =	$804.15		$889.4983	$889.49	$889.50	$889.50