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	$126.45	9.782%	$138.8193	$138.82	$138.80	$138.80
Purchase #2	$48.95	5.146%	$51.469	$51.47	$51.45	$51.50
Purchase #3	$66.37	4.427%	$69.3082	$69.31	$69.30	$69.30
Purchase #4	$113.38	12.424%	$127.4663	$127.47	$127.45	$127.50
Purchase #5	$86.30	6.451%	$91.8672	$91.87	$91.85	$91.90
Purchase #6	$154.40	7.362%	$165.7669	$165.77	$165.75	$165.80
Purchase #7	$72.53	13.172%	$82.0837	$82.08	$82.10	$82.10
7 purchase totals =	$668.38		$726.7806	$726.79	$726.70	$726.90