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	$24.85	3.354%	$25.6835	$25.68	$25.70	$25.70
Purchase #2	$57.45	3.289%	$59.3395	$59.34	$59.35	$59.30
Purchase #3	$86.42	5.489%	$91.1636	$91.16	$91.15	$91.20
Purchase #4	$241.64	8.741%	$262.7618	$262.76	$262.75	$262.80
Purchase #5	$152.39	5.396%	$160.613	$160.61	$160.60	$160.60
Purchase #6	$27.51	9.690%	$30.1757	$30.18	$30.20	$30.20
Purchase #7	$29.43	11.562%	$32.8327	$32.83	$32.85	$32.80
7 purchase totals =	$619.69		$662.5698	$662.56	$662.60	$662.60