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	$74.46	7.650%	$80.1562	$80.16	$80.15	$80.20
Purchase #2	$240.78	6.219%	$255.7541	$255.75	$255.75	$255.80
Purchase #3	$170.32	8.787%	$185.286	$185.29	$185.30	$185.30
Purchase #4	$108.43	7.192%	$116.2283	$116.23	$116.25	$116.20
Purchase #5	$166.35	11.481%	$185.4486	$185.45	$185.45	$185.40
Purchase #6	$8.28	5.776%	$8.7583	$8.76	$8.75	$8.80
Purchase #7	$235.83	10.800%	$261.2996	$261.30	$261.30	$261.30
7 purchase totals =	$1,004.45		$1,092.9311	$1,092.94	$1,092.95	$1,093.00