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	$40.66	3.655%	$42.1461	$42.15	$42.15	$42.10
Purchase #2	$94.40	11.195%	$104.9681	$104.97	$104.95	$105.00
Purchase #3	$98.92	10.806%	$109.6093	$109.61	$109.60	$109.60
Purchase #4	$207.87	11.261%	$231.2782	$231.28	$231.30	$231.30
Purchase #5	$129.42	11.642%	$144.4871	$144.49	$144.50	$144.50
Purchase #6	$235.34	9.869%	$258.5657	$258.57	$258.55	$258.60
Purchase #7	$74.41	11.543%	$82.9991	$83.00	$83.00	$83.00
7 purchase totals =	$881.02		$974.0536	$974.07	$974.05	$974.10