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	$32.55	4.584%	$34.0421	$34.04	$34.05	$34.00
Purchase #2	$82.80	8.745%	$90.0409	$90.04	$90.05	$90.00
Purchase #3	$218.48	9.345%	$238.897	$238.90	$238.90	$238.90
Purchase #4	$204.92	5.209%	$215.5943	$215.59	$215.60	$215.60
Purchase #5	$44.99	11.476%	$50.1531	$50.15	$50.15	$50.20
Purchase #6	$215.77	4.495%	$225.4689	$225.47	$225.45	$225.50
Purchase #7	$182.73	4.764%	$191.4353	$191.44	$191.45	$191.40
7 purchase totals =	$982.24		$1,045.6316	$1,045.63	$1,045.65	$1,045.60