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	$154.53	7.172%	$165.6129	$165.61	$165.60	$165.60
Purchase #2	$126.59	8.734%	$137.6464	$137.65	$137.65	$137.60
Purchase #3	$69.39	12.547%	$78.0964	$78.10	$78.10	$78.10
Purchase #4	$118.47	3.841%	$123.0204	$123.02	$123.00	$123.00
Purchase #5	$148.90	3.157%	$153.6008	$153.60	$153.60	$153.60
Purchase #6	$223.26	9.828%	$245.202	$245.20	$245.20	$245.20
Purchase #7	$79.39	9.211%	$86.7026	$86.70	$86.70	$86.70
7 purchase totals =	$920.53		$989.8815	$989.88	$989.85	$989.80