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	$89.60	11.854%	$100.2212	$100.22	$100.20	$100.20
Purchase #2	$53.30	11.748%	$59.5617	$59.56	$59.55	$59.60
Purchase #3	$86.40	8.167%	$93.4563	$93.46	$93.45	$93.50
Purchase #4	$211.73	10.165%	$233.2524	$233.25	$233.25	$233.30
Purchase #5	$211.59	13.561%	$240.2837	$240.28	$240.30	$240.30
Purchase #6	$218.34	12.657%	$245.9753	$245.98	$246.00	$246.00
Purchase #7	$248.95	9.274%	$272.0376	$272.04	$272.05	$272.00
7 purchase totals =	$1,119.91		$1,244.7882	$1,244.79	$1,244.80	$1,244.90