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	$128.38	10.769%	$142.2052	$142.21	$142.20	$142.20
Purchase #2	$77.79	9.801%	$85.4142	$85.41	$85.40	$85.40
Purchase #3	$122.56	11.779%	$136.9963	$137.00	$137.00	$137.00
Purchase #4	$38.58	13.462%	$43.7736	$43.77	$43.75	$43.80
Purchase #5	$20.45	4.623%	$21.3954	$21.40	$21.40	$21.40
Purchase #6	$42.58	8.558%	$46.224	$46.22	$46.20	$46.20
Purchase #7	$142.35	10.155%	$156.8056	$156.81	$156.80	$156.80
7 purchase totals =	$572.69		$632.8143	$632.82	$632.75	$632.80