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	$49.53	7.393%	$53.1918	$53.19	$53.20	$53.20
Purchase #2	$79.40	12.553%	$89.3671	$89.37	$89.35	$89.40
Purchase #3	$219.25	5.357%	$230.9952	$231.00	$231.00	$231.00
Purchase #4	$164.97	9.871%	$181.2542	$181.25	$181.25	$181.30
Purchase #5	$211.93	8.104%	$229.1048	$229.10	$229.10	$229.10
Purchase #6	$217.73	5.498%	$229.7008	$229.70	$229.70	$229.70
Purchase #7	$61.90	9.472%	$67.7632	$67.76	$67.75	$67.80
7 purchase totals =	$1,004.71		$1,081.3771	$1,081.37	$1,081.35	$1,081.50