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	$229.35	13.721%	$260.8191	$260.82	$260.80	$260.80
Purchase #2	$41.51	6.133%	$44.0558	$44.06	$44.05	$44.10
Purchase #3	$241.98	9.732%	$265.5295	$265.53	$265.55	$265.50
Purchase #4	$146.90	5.342%	$154.7474	$154.75	$154.75	$154.70
Purchase #5	$87.59	13.869%	$99.7379	$99.74	$99.75	$99.70
Purchase #6	$188.52	5.304%	$198.5191	$198.52	$198.50	$198.50
Purchase #7	$37.91	12.488%	$42.6442	$42.64	$42.65	$42.60
7 purchase totals =	$973.76		$1,066.0530	$1,066.06	$1,066.05	$1,065.90