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	$241.96	12.245%	$271.588	$271.59	$271.60	$271.60
Purchase #2	$153.41	11.224%	$170.6287	$170.63	$170.65	$170.60
Purchase #3	$108.37	6.675%	$115.6037	$115.60	$115.60	$115.60
Purchase #4	$85.86	3.669%	$89.0102	$89.01	$89.00	$89.00
Purchase #5	$13.53	8.735%	$14.7118	$14.71	$14.70	$14.70
Purchase #6	$160.90	5.108%	$169.1188	$169.12	$169.10	$169.10
Purchase #7	$35.29	7.318%	$37.8725	$37.87	$37.85	$37.90
7 purchase totals =	$799.32		$868.5337	$868.53	$868.50	$868.50