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	$145.45	3.448%	$150.4651	$150.47	$150.45	$150.50
Purchase #2	$188.73	13.172%	$213.5895	$213.59	$213.60	$213.60
Purchase #3	$139.36	4.628%	$145.8096	$145.81	$145.80	$145.80
Purchase #4	$132.69	7.262%	$142.3259	$142.33	$142.35	$142.30
Purchase #5	$189.78	5.815%	$200.8157	$200.82	$200.80	$200.80
Purchase #6	$63.68	6.472%	$67.8014	$67.80	$67.80	$67.80
Purchase #7	$242.45	5.128%	$254.8828	$254.88	$254.90	$254.90
7 purchase totals =	$1,102.14		$1,175.6900	$1,175.70	$1,175.70	$1,175.70