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	$129.82	5.176%	$136.5395	$136.54	$136.55	$136.50
Purchase #2	$48.81	7.611%	$52.5249	$52.52	$52.50	$52.50
Purchase #3	$130.34	10.778%	$144.388	$144.39	$144.40	$144.40
Purchase #4	$103.51	7.422%	$111.1925	$111.19	$111.20	$111.20
Purchase #5	$203.47	8.187%	$220.1281	$220.13	$220.15	$220.10
Purchase #6	$206.30	3.411%	$213.3369	$213.34	$213.35	$213.30
Purchase #7	$133.96	6.221%	$142.2937	$142.29	$142.30	$142.30
7 purchase totals =	$956.21		$1,020.4036	$1,020.40	$1,020.45	$1,020.30