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	$167.67	6.700%	$178.9039	$178.90	$178.90	$178.90
Purchase #2	$51.27	12.317%	$57.5849	$57.58	$57.60	$57.60
Purchase #3	$199.66	10.845%	$221.3131	$221.31	$221.30	$221.30
Purchase #4	$133.79	13.861%	$152.3346	$152.33	$152.35	$152.30
Purchase #5	$216.46	9.618%	$237.2791	$237.28	$237.30	$237.30
Purchase #6	$84.70	5.785%	$89.5999	$89.60	$89.60	$89.60
Purchase #7	$54.99	13.601%	$62.4692	$62.47	$62.45	$62.50
7 purchase totals =	$908.54		$999.4847	$999.47	$999.50	$999.50