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	$79.78	13.698%	$90.7083	$90.71	$90.70	$90.70
Purchase #2	$74.97	5.184%	$78.8564	$78.86	$78.85	$78.90
Purchase #3	$161.88	6.196%	$171.9101	$171.91	$171.90	$171.90
Purchase #4	$227.28	8.113%	$245.7192	$245.72	$245.70	$245.70
Purchase #5	$131.45	12.286%	$147.5999	$147.60	$147.60	$147.60
Purchase #6	$85.78	9.460%	$93.8948	$93.89	$93.90	$93.90
Purchase #7	$97.93	9.523%	$107.2559	$107.26	$107.25	$107.30
7 purchase totals =	$859.07		$935.9446	$935.95	$935.90	$936.00