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	$26.70	12.456%	$30.0258	$30.03	$30.05	$30.00
Purchase #2	$158.66	4.550%	$165.879	$165.88	$165.90	$165.90
Purchase #3	$96.38	10.361%	$106.3659	$106.37	$106.35	$106.40
Purchase #4	$7.72	10.416%	$8.5241	$8.52	$8.50	$8.50
Purchase #5	$39.69	6.563%	$42.2949	$42.29	$42.30	$42.30
Purchase #6	$218.34	11.213%	$242.8225	$242.82	$242.80	$242.80
Purchase #7	$214.96	11.141%	$238.9087	$238.91	$238.90	$238.90
7 purchase totals =	$762.45		$834.8209	$834.82	$834.80	$834.80