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	$7.27	10.663%	$8.0452	$8.05	$8.05	$8.00
Purchase #2	$140.97	6.440%	$150.0485	$150.05	$150.05	$150.00
Purchase #3	$143.42	4.594%	$150.0087	$150.01	$150.00	$150.00
Purchase #4	$12.63	3.272%	$13.0433	$13.04	$13.05	$13.00
Purchase #5	$76.28	3.106%	$78.6493	$78.65	$78.65	$78.60
Purchase #6	$132.77	10.648%	$146.9073	$146.91	$146.90	$146.90
Purchase #7	$196.76	13.634%	$223.5863	$223.59	$223.60	$223.60
7 purchase totals =	$710.10		$770.2886	$770.30	$770.30	$770.10