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	$73.48	13.569%	$83.4505	$83.45	$83.45	$83.50
Purchase #2	$169.37	4.179%	$176.448	$176.45	$176.45	$176.40
Purchase #3	$155.27	3.620%	$160.8908	$160.89	$160.90	$160.90
Purchase #4	$196.90	3.235%	$203.2697	$203.27	$203.25	$203.30
Purchase #5	$158.66	12.590%	$178.6353	$178.64	$178.65	$178.60
Purchase #6	$75.28	3.483%	$77.902	$77.90	$77.90	$77.90
Purchase #7	$37.76	8.142%	$40.8344	$40.83	$40.85	$40.80
7 purchase totals =	$866.72		$921.4307	$921.43	$921.45	$921.40