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	$250.50	3.569%	$259.4403	$259.44	$259.45	$259.40
Purchase #2	$41.83	11.200%	$46.515	$46.52	$46.50	$46.50
Purchase #3	$9.65	4.109%	$10.0465	$10.05	$10.05	$10.00
Purchase #4	$165.57	5.634%	$174.8982	$174.90	$174.90	$174.90
Purchase #5	$124.68	3.150%	$128.6074	$128.61	$128.60	$128.60
Purchase #6	$30.91	3.703%	$32.0546	$32.05	$32.05	$32.10
Purchase #7	$164.94	3.687%	$171.0213	$171.02	$171.00	$171.00
7 purchase totals =	$788.08		$822.5833	$822.59	$822.55	$822.50