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	$227.53	12.143%	$255.159	$255.16	$255.15	$255.20
Purchase #2	$126.72	12.236%	$142.2255	$142.23	$142.25	$142.20
Purchase #3	$227.64	12.418%	$255.9083	$255.91	$255.90	$255.90
Purchase #4	$62.36	6.613%	$66.4839	$66.48	$66.50	$66.50
Purchase #5	$139.31	3.502%	$144.1886	$144.19	$144.20	$144.20
Purchase #6	$196.54	3.847%	$204.1009	$204.10	$204.10	$204.10
Purchase #7	$184.33	9.219%	$201.3234	$201.32	$201.30	$201.30
7 purchase totals =	$1,164.43		$1,269.3896	$1,269.39	$1,269.40	$1,269.40