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	$236.95	9.191%	$258.7281	$258.73	$258.75	$258.70
Purchase #2	$195.95	13.711%	$222.8167	$222.82	$222.80	$222.80
Purchase #3	$154.52	11.606%	$172.4536	$172.45	$172.45	$172.50
Purchase #4	$143.46	3.523%	$148.5141	$148.51	$148.50	$148.50
Purchase #5	$201.72	3.557%	$208.8952	$208.90	$208.90	$208.90
Purchase #6	$41.88	12.351%	$47.0526	$47.05	$47.05	$47.10
Purchase #7	$136.44	6.705%	$145.5883	$145.59	$145.60	$145.60
7 purchase totals =	$1,110.92		$1,204.0486	$1,204.05	$1,204.05	$1,204.10