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	$130.77	5.309%	$137.7126	$137.71	$137.70	$137.70
Purchase #2	$32.25	3.106%	$33.2517	$33.25	$33.25	$33.30
Purchase #3	$132.84	8.353%	$143.9361	$143.94	$143.95	$143.90
Purchase #4	$149.75	3.584%	$155.117	$155.12	$155.10	$155.10
Purchase #5	$229.68	4.730%	$240.5439	$240.54	$240.55	$240.50
Purchase #6	$168.61	12.324%	$189.3895	$189.39	$189.40	$189.40
Purchase #7	$37.74	12.393%	$42.4171	$42.42	$42.40	$42.40
7 purchase totals =	$881.64		$942.3679	$942.37	$942.35	$942.30