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	$232.36	10.735%	$257.3038	$257.30	$257.30	$257.30
Purchase #2	$42.74	11.398%	$47.6115	$47.61	$47.60	$47.60
Purchase #3	$81.58	10.433%	$90.0912	$90.09	$90.10	$90.10
Purchase #4	$38.86	11.358%	$43.2737	$43.27	$43.25	$43.30
Purchase #5	$116.35	6.113%	$123.4625	$123.46	$123.45	$123.50
Purchase #6	$84.50	3.606%	$87.5471	$87.55	$87.55	$87.50
Purchase #7	$215.76	4.407%	$225.2685	$225.27	$225.25	$225.30
7 purchase totals =	$812.15		$874.5583	$874.55	$874.50	$874.60