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	$241.42	13.595%	$274.241	$274.24	$274.25	$274.20
Purchase #2	$100.73	12.566%	$113.3877	$113.39	$113.40	$113.40
Purchase #3	$223.41	3.642%	$231.5466	$231.55	$231.55	$231.50
Purchase #4	$120.93	12.776%	$136.38	$136.38	$136.40	$136.40
Purchase #5	$250.51	3.609%	$259.5509	$259.55	$259.55	$259.60
Purchase #6	$174.94	12.495%	$196.7988	$196.80	$196.80	$196.80
Purchase #7	$112.95	12.663%	$127.2529	$127.25	$127.25	$127.30
7 purchase totals =	$1,224.89		$1,339.1579	$1,339.16	$1,339.20	$1,339.20