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	$238.81	13.254%	$270.4619	$270.46	$270.45	$270.50
Purchase #2	$138.61	5.615%	$146.393	$146.39	$146.40	$146.40
Purchase #3	$94.82	11.755%	$105.9661	$105.97	$105.95	$106.00
Purchase #4	$231.30	12.844%	$261.0082	$261.01	$261.00	$261.00
Purchase #5	$103.85	4.419%	$108.4391	$108.44	$108.45	$108.40
Purchase #6	$44.53	9.640%	$48.8227	$48.82	$48.80	$48.80
Purchase #7	$104.47	4.219%	$108.8776	$108.88	$108.90	$108.90
7 purchase totals =	$956.39		$1,049.9686	$1,049.97	$1,049.95	$1,050.00