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	$93.47	11.673%	$104.3808	$104.38	$104.40	$104.40
Purchase #2	$94.97	4.770%	$99.5001	$99.50	$99.50	$99.50
Purchase #3	$172.80	10.808%	$191.4762	$191.48	$191.50	$191.50
Purchase #4	$244.96	8.582%	$265.9825	$265.98	$266.00	$266.00
Purchase #5	$230.49	6.633%	$245.7784	$245.78	$245.80	$245.80
Purchase #6	$215.42	13.449%	$244.3918	$244.39	$244.40	$244.40
Purchase #7	$219.61	10.169%	$241.9421	$241.94	$241.95	$241.90
7 purchase totals =	$1,271.72		$1,393.4519	$1,393.45	$1,393.55	$1,393.50