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	$90.93	4.825%	$95.3174	$95.32	$95.30	$95.30
Purchase #2	$73.34	9.282%	$80.1474	$80.15	$80.15	$80.10
Purchase #3	$246.33	3.710%	$255.4688	$255.47	$255.45	$255.50
Purchase #4	$92.65	10.718%	$102.5802	$102.58	$102.60	$102.60
Purchase #5	$34.56	11.122%	$38.4038	$38.40	$38.40	$38.40
Purchase #6	$59.63	9.303%	$65.1774	$65.18	$65.20	$65.20
Purchase #7	$50.32	11.365%	$56.0389	$56.04	$56.05	$56.00
7 purchase totals =	$647.76		$693.1339	$693.14	$693.15	$693.10