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	$19.62	4.646%	$20.5315	$20.53	$20.55	$20.50
Purchase #2	$72.77	11.157%	$80.8889	$80.89	$80.90	$80.90
Purchase #3	$72.59	8.687%	$78.8959	$78.90	$78.90	$78.90
Purchase #4	$94.52	4.419%	$98.6968	$98.70	$98.70	$98.70
Purchase #5	$234.63	13.439%	$266.1619	$266.16	$266.15	$266.20
Purchase #6	$211.67	6.426%	$225.2719	$225.27	$225.25	$225.30
Purchase #7	$220.29	7.836%	$237.5519	$237.55	$237.55	$237.60
7 purchase totals =	$926.09		$1,007.9988	$1,008.00	$1,008.00	$1,008.10