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	$7.99	13.328%	$9.0549	$9.05	$9.05	$9.10
Purchase #2	$100.70	10.355%	$111.1275	$111.13	$111.15	$111.10
Purchase #3	$191.57	7.834%	$206.5776	$206.58	$206.60	$206.60
Purchase #4	$51.50	3.476%	$53.2901	$53.29	$53.30	$53.30
Purchase #5	$97.70	3.297%	$100.9212	$100.92	$100.90	$100.90
Purchase #6	$171.93	10.319%	$189.6715	$189.67	$189.65	$189.70
Purchase #7	$136.67	10.437%	$150.9342	$150.93	$150.95	$150.90
7 purchase totals =	$758.06		$821.5770	$821.57	$821.60	$821.60