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	$145.38	4.206%	$151.4947	$151.49	$151.50	$151.50
Purchase #2	$178.50	11.676%	$199.3417	$199.34	$199.35	$199.30
Purchase #3	$199.91	4.743%	$209.3917	$209.39	$209.40	$209.40
Purchase #4	$108.63	13.219%	$122.9898	$122.99	$123.00	$123.00
Purchase #5	$109.35	9.255%	$119.4703	$119.47	$119.45	$119.50
Purchase #6	$136.97	3.698%	$142.0352	$142.04	$142.05	$142.00
Purchase #7	$11.59	10.816%	$12.8436	$12.84	$12.85	$12.80
7 purchase totals =	$890.33		$957.5670	$957.56	$957.60	$957.50