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	$182.57	11.574%	$203.7007	$203.70	$203.70	$203.70
Purchase #2	$57.50	8.763%	$62.5387	$62.54	$62.55	$62.50
Purchase #3	$204.78	9.164%	$223.546	$223.55	$223.55	$223.50
Purchase #4	$221.59	11.188%	$246.3815	$246.38	$246.40	$246.40
Purchase #5	$99.34	12.477%	$111.7347	$111.73	$111.75	$111.70
Purchase #6	$191.60	11.820%	$214.2471	$214.25	$214.25	$214.20
Purchase #7	$234.38	10.184%	$258.2493	$258.25	$258.25	$258.20
7 purchase totals =	$1,191.76		$1,320.3980	$1,320.40	$1,320.45	$1,320.20