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	$116.89	11.867%	$130.7613	$130.76	$130.75	$130.80
Purchase #2	$35.63	9.339%	$38.9575	$38.96	$38.95	$39.00
Purchase #3	$91.82	9.445%	$100.4924	$100.49	$100.50	$100.50
Purchase #4	$62.85	4.753%	$65.8373	$65.84	$65.85	$65.80
Purchase #5	$144.50	4.220%	$150.5979	$150.60	$150.60	$150.60
Purchase #6	$237.41	10.648%	$262.6894	$262.69	$262.70	$262.70
Purchase #7	$67.61	5.688%	$71.4557	$71.46	$71.45	$71.50
7 purchase totals =	$756.71		$820.7915	$820.80	$820.80	$820.90