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	$104.43	11.851%	$116.806	$116.81	$116.80	$116.80
Purchase #2	$127.38	8.872%	$138.6812	$138.68	$138.70	$138.70
Purchase #3	$26.40	7.214%	$28.3045	$28.30	$28.30	$28.30
Purchase #4	$167.48	10.758%	$185.4975	$185.50	$185.50	$185.50
Purchase #5	$119.64	9.824%	$131.3934	$131.39	$131.40	$131.40
Purchase #6	$165.74	4.464%	$173.1386	$173.14	$173.15	$173.10
Purchase #7	$65.32	10.272%	$72.0297	$72.03	$72.05	$72.00
7 purchase totals =	$776.39		$845.8509	$845.85	$845.90	$845.80