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	$205.36	8.473%	$222.7602	$222.76	$222.75	$222.80
Purchase #2	$30.53	5.569%	$32.2302	$32.23	$32.25	$32.20
Purchase #3	$10.85	12.532%	$12.2097	$12.21	$12.20	$12.20
Purchase #4	$88.69	7.585%	$95.4171	$95.42	$95.40	$95.40
Purchase #5	$88.89	11.546%	$99.1532	$99.15	$99.15	$99.20
Purchase #6	$151.31	11.254%	$168.3384	$168.34	$168.35	$168.30
Purchase #7	$17.87	11.810%	$19.9804	$19.98	$20.00	$20.00
7 purchase totals =	$593.50		$650.0892	$650.09	$650.10	$650.10