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	$156.88	4.784%	$164.3851	$164.39	$164.40	$164.40
Purchase #2	$58.54	3.759%	$60.7405	$60.74	$60.75	$60.70
Purchase #3	$234.28	13.462%	$265.8188	$265.82	$265.80	$265.80
Purchase #4	$162.35	3.783%	$168.4917	$168.49	$168.50	$168.50
Purchase #5	$17.71	6.557%	$18.8712	$18.87	$18.85	$18.90
Purchase #6	$197.98	6.714%	$211.2724	$211.27	$211.25	$211.30
Purchase #7	$162.40	3.537%	$168.1441	$168.14	$168.15	$168.10
7 purchase totals =	$990.14		$1,057.7238	$1,057.72	$1,057.70	$1,057.70