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	$68.47	12.637%	$77.1226	$77.12	$77.10	$77.10
Purchase #2	$247.72	13.685%	$281.6205	$281.62	$281.60	$281.60
Purchase #3	$229.27	11.778%	$256.2734	$256.27	$256.25	$256.30
Purchase #4	$115.26	4.854%	$120.8547	$120.85	$120.85	$120.90
Purchase #5	$9.43	5.499%	$9.9486	$9.95	$9.95	$9.90
Purchase #6	$86.49	4.615%	$90.4815	$90.48	$90.50	$90.50
Purchase #7	$238.91	4.836%	$250.4637	$250.46	$250.45	$250.50
7 purchase totals =	$995.55		$1,086.7650	$1,086.75	$1,086.70	$1,086.80