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	$7.69	3.129%	$7.9306	$7.93	$7.95	$7.90
Purchase #2	$173.71	13.312%	$196.8343	$196.83	$196.85	$196.80
Purchase #3	$27.76	12.347%	$31.1875	$31.19	$31.20	$31.20
Purchase #4	$139.25	8.757%	$151.4441	$151.44	$151.45	$151.40
Purchase #5	$55.81	4.687%	$58.4258	$58.43	$58.45	$58.40
Purchase #6	$32.35	13.104%	$36.5891	$36.59	$36.60	$36.60
Purchase #7	$220.55	8.199%	$238.6329	$238.63	$238.65	$238.60
7 purchase totals =	$657.12		$721.0443	$721.04	$721.15	$720.90