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	$128.99	11.546%	$143.8832	$143.88	$143.90	$143.90
Purchase #2	$72.84	13.685%	$82.8082	$82.81	$82.80	$82.80
Purchase #3	$174.58	6.237%	$185.4686	$185.47	$185.45	$185.50
Purchase #4	$15.83	11.736%	$17.6878	$17.69	$17.70	$17.70
Purchase #5	$180.47	6.318%	$191.8721	$191.87	$191.85	$191.90
Purchase #6	$247.72	13.386%	$280.8798	$280.88	$280.90	$280.90
Purchase #7	$208.36	12.626%	$234.6675	$234.67	$234.65	$234.70
7 purchase totals =	$1,028.79		$1,137.2672	$1,137.27	$1,137.25	$1,137.40