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	$101.80	12.531%	$114.5566	$114.56	$114.55	$114.60
Purchase #2	$113.57	8.560%	$123.2916	$123.29	$123.30	$123.30
Purchase #3	$102.45	7.463%	$110.0958	$110.10	$110.10	$110.10
Purchase #4	$29.79	12.527%	$33.5218	$33.52	$33.50	$33.50
Purchase #5	$64.86	10.732%	$71.8208	$71.82	$71.80	$71.80
Purchase #6	$133.58	6.745%	$142.59	$142.59	$142.60	$142.60
Purchase #7	$99.42	8.585%	$107.9552	$107.96	$107.95	$108.00
7 purchase totals =	$645.47		$703.8318	$703.84	$703.80	$703.90