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	$92.97	3.107%	$95.8586	$95.86	$95.85	$95.90
Purchase #2	$88.81	12.641%	$100.0365	$100.04	$100.05	$100.00
Purchase #3	$114.30	11.843%	$127.8365	$127.84	$127.85	$127.80
Purchase #4	$70.63	10.689%	$78.1796	$78.18	$78.20	$78.20
Purchase #5	$19.64	13.493%	$22.29	$22.29	$22.30	$22.30
Purchase #6	$62.80	6.572%	$66.9272	$66.93	$66.95	$66.90
Purchase #7	$148.50	13.810%	$169.0079	$169.01	$169.00	$169.00
7 purchase totals =	$597.65		$660.1363	$660.15	$660.20	$660.10