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	$184.75	10.470%	$204.0933	$204.09	$204.10	$204.10
Purchase #2	$156.83	6.673%	$167.2953	$167.30	$167.30	$167.30
Purchase #3	$101.91	7.658%	$109.7143	$109.71	$109.70	$109.70
Purchase #4	$130.78	8.668%	$142.116	$142.12	$142.10	$142.10
Purchase #5	$158.29	6.375%	$168.381	$168.38	$168.40	$168.40
Purchase #6	$82.29	9.738%	$90.3034	$90.30	$90.30	$90.30
Purchase #7	$90.30	12.692%	$101.7609	$101.76	$101.75	$101.80
7 purchase totals =	$905.15		$983.6642	$983.66	$983.65	$983.70