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	$28.82	8.547%	$31.2832	$31.28	$31.30	$31.30
Purchase #2	$166.62	7.334%	$178.8399	$178.84	$178.85	$178.80
Purchase #3	$197.47	11.623%	$220.4219	$220.42	$220.40	$220.40
Purchase #4	$222.71	7.811%	$240.1059	$240.11	$240.10	$240.10
Purchase #5	$134.65	3.857%	$139.8435	$139.84	$139.85	$139.80
Purchase #6	$50.27	9.870%	$55.2316	$55.23	$55.25	$55.20
Purchase #7	$177.78	4.587%	$185.9348	$185.93	$185.95	$185.90
7 purchase totals =	$978.32		$1,051.6608	$1,051.65	$1,051.70	$1,051.50