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	$104.88	8.583%	$113.8819	$113.88	$113.90	$113.90
Purchase #2	$55.78	3.653%	$57.8176	$57.82	$57.80	$57.80
Purchase #3	$160.98	7.788%	$173.5171	$173.52	$173.50	$173.50
Purchase #4	$114.47	7.841%	$123.4456	$123.45	$123.45	$123.40
Purchase #5	$91.91	10.336%	$101.4098	$101.41	$101.40	$101.40
Purchase #6	$72.31	10.403%	$79.8324	$79.83	$79.85	$79.80
Purchase #7	$64.47	9.295%	$70.4625	$70.46	$70.45	$70.50
7 purchase totals =	$664.80		$720.3669	$720.37	$720.35	$720.30