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	$206.96	13.309%	$234.5043	$234.50	$234.50	$234.50
Purchase #2	$88.25	3.217%	$91.089	$91.09	$91.10	$91.10
Purchase #3	$31.69	10.375%	$34.9778	$34.98	$35.00	$35.00
Purchase #4	$140.56	5.506%	$148.2992	$148.30	$148.30	$148.30
Purchase #5	$241.72	10.265%	$266.5326	$266.53	$266.55	$266.50
Purchase #6	$80.65	12.164%	$90.4603	$90.46	$90.45	$90.50
Purchase #7	$214.93	4.745%	$225.1284	$225.13	$225.15	$225.10
7 purchase totals =	$1,004.76		$1,090.9916	$1,090.99	$1,091.05	$1,091.00