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	$66.71	4.759%	$69.8847	$69.88	$69.90	$69.90
Purchase #2	$150.64	11.821%	$168.4472	$168.45	$168.45	$168.40
Purchase #3	$225.63	5.774%	$238.6579	$238.66	$238.65	$238.70
Purchase #4	$66.27	10.205%	$73.0329	$73.03	$73.05	$73.00
Purchase #5	$246.51	11.841%	$275.6992	$275.70	$275.70	$275.70
Purchase #6	$144.76	13.713%	$164.6109	$164.61	$164.60	$164.60
Purchase #7	$38.38	3.470%	$39.7118	$39.71	$39.70	$39.70
7 purchase totals =	$938.90		$1,030.0446	$1,030.04	$1,030.05	$1,030.00