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	$245.50	10.761%	$271.9183	$271.92	$271.90	$271.90
Purchase #2	$93.49	9.639%	$102.5015	$102.50	$102.50	$102.50
Purchase #3	$206.54	12.104%	$231.5396	$231.54	$231.55	$231.50
Purchase #4	$114.42	8.748%	$124.4295	$124.43	$124.45	$124.40
Purchase #5	$197.40	12.669%	$222.4086	$222.41	$222.40	$222.40
Purchase #6	$82.43	3.447%	$85.2714	$85.27	$85.25	$85.30
Purchase #7	$78.75	12.575%	$88.6528	$88.65	$88.65	$88.70
7 purchase totals =	$1,018.53		$1,126.7217	$1,126.72	$1,126.70	$1,126.70