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	$39.91	3.315%	$41.233	$41.23	$41.25	$41.20
Purchase #2	$82.80	8.778%	$90.0682	$90.07	$90.05	$90.10
Purchase #3	$177.55	9.514%	$194.4421	$194.44	$194.45	$194.40
Purchase #4	$114.57	5.489%	$120.8587	$120.86	$120.85	$120.90
Purchase #5	$112.93	4.511%	$118.0243	$118.02	$118.00	$118.00
Purchase #6	$130.68	9.287%	$142.8163	$142.82	$142.80	$142.80
Purchase #7	$86.45	13.429%	$98.0594	$98.06	$98.05	$98.10
7 purchase totals =	$744.89		$805.5020	$805.50	$805.45	$805.50