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	$126.46	9.152%	$138.0336	$138.03	$138.05	$138.00
Purchase #2	$233.76	9.251%	$255.3851	$255.39	$255.40	$255.40
Purchase #3	$156.39	12.749%	$176.3282	$176.33	$176.35	$176.30
Purchase #4	$167.69	8.488%	$181.9235	$181.92	$181.90	$181.90
Purchase #5	$97.56	12.199%	$109.4613	$109.46	$109.45	$109.50
Purchase #6	$47.97	9.395%	$52.4768	$52.48	$52.50	$52.50
Purchase #7	$77.63	7.324%	$83.3156	$83.32	$83.30	$83.30
7 purchase totals =	$907.46		$996.9241	$996.93	$996.95	$996.90