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	$32.97	12.380%	$37.0517	$37.05	$37.05	$37.10
Purchase #2	$205.58	10.856%	$227.8978	$227.90	$227.90	$227.90
Purchase #3	$24.85	10.409%	$27.4366	$27.44	$27.45	$27.40
Purchase #4	$77.47	7.743%	$83.4685	$83.47	$83.45	$83.50
Purchase #5	$219.74	8.127%	$237.5983	$237.60	$237.60	$237.60
Purchase #6	$115.78	10.139%	$127.5189	$127.52	$127.50	$127.50
Purchase #7	$6.94	6.543%	$7.3941	$7.39	$7.40	$7.40
7 purchase totals =	$683.33		$748.3659	$748.37	$748.35	$748.40