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	$79.79	13.619%	$90.6566	$90.66	$90.65	$90.70
Purchase #2	$82.76	12.604%	$93.1911	$93.19	$93.20	$93.20
Purchase #3	$11.77	13.582%	$13.3686	$13.37	$13.35	$13.40
Purchase #4	$102.71	9.484%	$112.451	$112.45	$112.45	$112.50
Purchase #5	$126.33	11.470%	$140.8201	$140.82	$140.80	$140.80
Purchase #6	$63.71	6.595%	$67.9117	$67.91	$67.90	$67.90
Purchase #7	$119.80	13.567%	$136.0533	$136.05	$136.05	$136.10
7 purchase totals =	$586.87		$654.4524	$654.45	$654.40	$654.60