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	$200.50	10.768%	$222.0898	$222.09	$222.10	$222.10
Purchase #2	$160.84	12.308%	$180.6362	$180.64	$180.65	$180.60
Purchase #3	$155.90	3.215%	$160.9122	$160.91	$160.90	$160.90
Purchase #4	$33.65	13.295%	$38.1238	$38.12	$38.10	$38.10
Purchase #5	$72.29	13.466%	$82.0246	$82.02	$82.00	$82.00
Purchase #6	$84.72	4.577%	$88.5976	$88.60	$88.60	$88.60
Purchase #7	$181.54	10.638%	$200.8522	$200.85	$200.85	$200.90
7 purchase totals =	$889.44		$973.2364	$973.23	$973.20	$973.20