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	$99.35	12.312%	$111.582	$111.58	$111.60	$111.60
Purchase #2	$46.97	9.446%	$51.4068	$51.41	$51.40	$51.40
Purchase #3	$86.35	10.624%	$95.5238	$95.52	$95.50	$95.50
Purchase #4	$249.57	7.697%	$268.7794	$268.78	$268.80	$268.80
Purchase #5	$88.44	13.171%	$100.0884	$100.09	$100.10	$100.10
Purchase #6	$149.43	10.825%	$165.6058	$165.61	$165.60	$165.60
Purchase #7	$31.91	11.294%	$35.5139	$35.51	$35.50	$35.50
7 purchase totals =	$752.02		$828.5001	$828.50	$828.50	$828.50