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	$125.86	10.550%	$139.1382	$139.14	$139.15	$139.10
Purchase #2	$146.41	9.590%	$160.4507	$160.45	$160.45	$160.50
Purchase #3	$194.35	13.348%	$220.2918	$220.29	$220.30	$220.30
Purchase #4	$31.63	13.219%	$35.8112	$35.81	$35.80	$35.80
Purchase #5	$241.67	10.591%	$267.2653	$267.27	$267.25	$267.30
Purchase #6	$19.57	10.474%	$21.6198	$21.62	$21.60	$21.60
Purchase #7	$56.37	5.564%	$59.5064	$59.51	$59.50	$59.50
7 purchase totals =	$815.86		$904.0834	$904.09	$904.05	$904.10